Attachment 245300 Details for Bug 140435 – Patch

[patch] Patch

bug-140435-20150125182106.patch (text/plain), 129.45 KB, created by Yusuke Suzuki on 2015-01-25 01:21:06 PST

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Creator: Yusuke Suzuki

Created: 2015-01-25 01:21:06 PST

Size: 129.45 KB

patch

obsolete

>Subversion Revision: 179084
>diff --git a/Source/JavaScriptCore/ChangeLog b/Source/JavaScriptCore/ChangeLog
>index f78ab7e58f82e675478a23cb8b62f2e1a8caa229..4fa05bccde16fd5b72d836b2d20d833ec6b048b8 100644
>--- a/Source/JavaScriptCore/ChangeLog
>+++ b/Source/JavaScriptCore/ChangeLog
>@@ -1,3 +1,149 @@
>+2015-01-25  Yusuke Suzuki  <utatane.tea@gmail.com>
>+
>+        Implement ES6 Symbol
>+        https://bugs.webkit.org/show_bug.cgi?id=140435
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * CMakeLists.txt:
>+        * DerivedSources.make:
>+        * JavaScriptCore.order:
>+        * JavaScriptCore.vcxproj/JavaScriptCore.vcxproj:
>+        * JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters:
>+        * JavaScriptCore.xcodeproj/project.pbxproj:
>+        * builtins/BuiltinExecutables.cpp:
>+        (JSC::BuiltinExecutables::createBuiltinExecutable):
>+        * builtins/BuiltinNames.h:
>+        * dfg/DFGOperations.cpp:
>+        (JSC::DFG::operationPutByValInternal):
>+        * interpreter/Interpreter.cpp:
>+        * jit/JITOperations.cpp:
>+        (JSC::getByVal):
>+        * llint/LLIntData.cpp:
>+        (JSC::LLInt::Data::performAssertions):
>+        * llint/LLIntSlowPaths.cpp:
>+        (JSC::LLInt::getByVal):
>+        (JSC::LLInt::LLINT_SLOW_PATH_DECL):
>+        * llint/LowLevelInterpreter.asm:
>+        * runtime/CommonIdentifiers.h:
>+        * runtime/CommonSlowPaths.cpp:
>+        (JSC::SLOW_PATH_DECL):
>+        * runtime/CommonSlowPaths.h:
>+        (JSC::CommonSlowPaths::opIn):
>+        * runtime/ExceptionHelpers.cpp:
>+        (JSC::createUndefinedVariableError):
>+        * runtime/JSCJSValue.cpp:
>+        (JSC::JSValue::synthesizePrototype):
>+        (JSC::JSValue::dumpInContextAssumingStructure):
>+        (JSC::JSValue::toStringSlowCase):
>+        * runtime/JSCJSValue.h:
>+        * runtime/JSCJSValueInlines.h:
>+        (JSC::JSValue::isSymbol):
>+        (JSC::JSValue::isPrimitive):
>+        (JSC::JSValue::toPropertyKey):
>+        (JSC::JSValue::getPropertySlot):
>+        (JSC::JSValue::get):
>+        (JSC::JSValue::equalSlowCaseInline):
>+        (JSC::JSValue::strictEqualSlowCaseInline):
>+        * runtime/JSCell.cpp:
>+        (JSC::JSCell::put):
>+        (JSC::JSCell::putByIndex):
>+        (JSC::JSCell::toPrimitive):
>+        (JSC::JSCell::getPrimitiveNumber):
>+        (JSC::JSCell::toNumber):
>+        (JSC::JSCell::toObject):
>+        * runtime/JSCell.h:
>+        * runtime/JSCellInlines.h:
>+        (JSC::JSCell::isSymbol):
>+        (JSC::JSCell::toBoolean):
>+        (JSC::JSCell::pureToBoolean):
>+        * runtime/JSGlobalObject.cpp:
>+        (JSC::JSGlobalObject::init):
>+        (JSC::JSGlobalObject::visitChildren):
>+        * runtime/JSGlobalObject.h:
>+        (JSC::JSGlobalObject::symbolPrototype):
>+        (JSC::JSGlobalObject::symbolObjectStructure):
>+        * runtime/JSONObject.cpp:
>+        (JSC::Stringifier::Stringifier):
>+        * runtime/JSSymbolTableObject.cpp:
>+        (JSC::JSSymbolTableObject::getOwnNonIndexPropertyNames):
>+        * runtime/JSType.h:
>+        * runtime/JSTypeInfo.h:
>+        (JSC::TypeInfo::isName): Deleted.
>+        * runtime/NameInstance.h: Removed.
>+        * runtime/NamePrototype.cpp: Removed.
>+        * runtime/ObjectConstructor.cpp:
>+        (JSC::objectConstructorGetOwnPropertyDescriptor):
>+        (JSC::objectConstructorDefineProperty):
>+        * runtime/ObjectPrototype.cpp:
>+        (JSC::objectProtoFuncHasOwnProperty):
>+        (JSC::objectProtoFuncDefineGetter):
>+        (JSC::objectProtoFuncDefineSetter):
>+        (JSC::objectProtoFuncLookupGetter):
>+        (JSC::objectProtoFuncLookupSetter):
>+        (JSC::objectProtoFuncPropertyIsEnumerable):
>+        * runtime/Operations.cpp:
>+        (JSC::jsTypeStringForValue):
>+        (JSC::jsIsObjectType):
>+        * runtime/PrivateName.h:
>+        (JSC::PrivateName::PrivateName):
>+        * runtime/PropertyMapHashTable.h:
>+        (JSC::PropertyTable::find):
>+        (JSC::PropertyTable::get):
>+        * runtime/PropertyName.h:
>+        (JSC::PropertyName::PropertyName):
>+        (JSC::PropertyName::publicName):
>+        * runtime/SmallStrings.h:
>+        * runtime/Structure.cpp:
>+        (JSC::Structure::getPropertyNamesFromStructure):
>+        * runtime/StructureInlines.h:
>+        (JSC::Structure::prototypeForLookup):
>+        * runtime/Symbol.cpp: Added.
>+        (JSC::Symbol::Symbol):
>+        (JSC::SymbolObject::create):
>+        (JSC::Symbol::toPrimitive):
>+        (JSC::Symbol::toBoolean):
>+        (JSC::Symbol::getPrimitiveNumber):
>+        (JSC::Symbol::toObject):
>+        (JSC::Symbol::toNumber):
>+        (JSC::Symbol::destroy):
>+        * runtime/Symbol.h: Added.
>+        (JSC::Symbol::createStructure):
>+        (JSC::Symbol::create):
>+        (JSC::Symbol::privateName):
>+        (JSC::Symbol::description):
>+        (JSC::Symbol::finishCreation):
>+        (JSC::asSymbol):
>+        * runtime/SymbolConstructor.cpp: Renamed from Source/JavaScriptCore/runtime/NameConstructor.cpp.
>+        (JSC::SymbolConstructor::SymbolConstructor):
>+        (JSC::SymbolConstructor::finishCreation):
>+        (JSC::callSymbol):
>+        (JSC::constructSymbol):
>+        (JSC::SymbolConstructor::getConstructData):
>+        (JSC::SymbolConstructor::getCallData):
>+        * runtime/SymbolConstructor.h: Renamed from Source/JavaScriptCore/runtime/NameConstructor.h.
>+        (JSC::SymbolConstructor::create):
>+        (JSC::SymbolConstructor::createStructure):
>+        * runtime/SymbolObject.cpp: Renamed from Source/JavaScriptCore/runtime/NameInstance.cpp.
>+        (JSC::SymbolObject::SymbolObject):
>+        (JSC::SymbolObject::finishCreation):
>+        * runtime/SymbolObject.h: Added.
>+        (JSC::SymbolObject::create):
>+        (JSC::SymbolObject::internalValue):
>+        (JSC::SymbolObject::createStructure):
>+        * runtime/SymbolPrototype.cpp: Added.
>+        (JSC::SymbolPrototype::SymbolPrototype):
>+        (JSC::SymbolPrototype::finishCreation):
>+        (JSC::SymbolPrototype::getOwnPropertySlot):
>+        (JSC::symbolProtoFuncToString):
>+        (JSC::symbolProtoFuncValueOf):
>+        * runtime/SymbolPrototype.h: Renamed from Source/JavaScriptCore/runtime/NamePrototype.h.
>+        (JSC::SymbolPrototype::create):
>+        (JSC::SymbolPrototype::createStructure):
>+        * runtime/VM.cpp:
>+        (JSC::VM::VM):
>+        * runtime/VM.h:
>+
> 2015-01-23  Joseph Pecoraro  <pecoraro@apple.com>
> 
>         Web Inspector: Rename InjectedScriptHost::type to subtype
>diff --git a/Source/WTF/ChangeLog b/Source/WTF/ChangeLog
>index f8b9597298239b2cf862c5626a31f22ef8846373..b062569c84b31409e72b776259ad52a756e631d9 100644
>--- a/Source/WTF/ChangeLog
>+++ b/Source/WTF/ChangeLog
>@@ -1,3 +1,25 @@
>+2015-01-25  Yusuke Suzuki  <utatane.tea@gmail.com>
>+
>+        Implement ES6 Symbol
>+        https://bugs.webkit.org/show_bug.cgi?id=140435
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * wtf/text/StringImpl.cpp:
>+        (WTF::StringImpl::~StringImpl):
>+        * wtf/text/StringImpl.h:
>+        (WTF::StringImpl::StringImpl):
>+        (WTF::StringImpl::createUniqueEmpty):
>+        (WTF::StringImpl::createUnique):
>+        (WTF::StringImpl::flagIsUnique):
>+        (WTF::StringImpl::isUnique):
>+        (WTF::StringImpl::setIsAtomic):
>+        (WTF::StringImpl::createEmptyUnique): Deleted.
>+        (WTF::StringImpl::isEmptyUnique): Deleted.
>+        * wtf/text/StringStatics.cpp:
>+        (WTF::StringImpl::hashAndFlagsForUnique):
>+        (WTF::StringImpl::hashAndFlagsForEmptyUnique): Deleted.
>+
> 2015-01-24  Chris Dumez  <cdumez@apple.com>
> 
>         Provide implementation for WTF::DefaultHash<bool>
>diff --git a/Source/JavaScriptCore/CMakeLists.txt b/Source/JavaScriptCore/CMakeLists.txt
>index 61cda2202aadb30a898d13c33509f6c7263bc5d5..5ef6a860eebf79a9d4a98076c898ba31a3bf0379 100644
>--- a/Source/JavaScriptCore/CMakeLists.txt
>+++ b/Source/JavaScriptCore/CMakeLists.txt
>@@ -508,9 +508,6 @@ set(JavaScriptCore_RUNTIME_SOURCES
>     runtime/MapPrototype.cpp
>     runtime/MathObject.cpp
>     runtime/MemoryStatistics.cpp
>-    runtime/NameConstructor.cpp
>-    runtime/NameInstance.cpp
>-    runtime/NamePrototype.cpp
>     runtime/NativeErrorConstructor.cpp
>     runtime/NativeErrorPrototype.cpp
>     runtime/NullGetterFunction.cpp
>@@ -551,6 +548,10 @@ set(JavaScriptCore_RUNTIME_SOURCES
>     runtime/StructureChain.cpp
>     runtime/StructureIDTable.cpp
>     runtime/StructureRareData.cpp
>+    runtime/Symbol.cpp
>+    runtime/SymbolObject.cpp
>+    runtime/SymbolPrototype.cpp
>+    runtime/SymbolConstructor.cpp
>     runtime/SymbolTable.cpp
>     runtime/TestRunnerUtils.cpp
>     runtime/TypeLocationCache.cpp
>@@ -584,7 +585,6 @@ set(JavaScriptCore_LUT_FILES
>     runtime/JSONObject.cpp
>     runtime/JSPromiseConstructor.cpp
>     runtime/JSPromisePrototype.cpp
>-    runtime/NamePrototype.cpp
>     runtime/NumberConstructor.cpp
>     runtime/NumberPrototype.cpp
>     runtime/ObjectConstructor.cpp
>@@ -592,6 +592,7 @@ set(JavaScriptCore_LUT_FILES
>     runtime/RegExpObject.cpp
>     runtime/RegExpPrototype.cpp
>     runtime/StringConstructor.cpp
>+    runtime/SymbolPrototype.cpp
> )
> 
> set(JavaScriptCore_LIBRARIES
>diff --git a/Source/JavaScriptCore/DerivedSources.make b/Source/JavaScriptCore/DerivedSources.make
>index 12afea24a6ee56a60dc5b82efbf06c42ab30dc44..4a2623ef5c9c756d5da547f1d3d65cea9a17695a 100644
>--- a/Source/JavaScriptCore/DerivedSources.make
>+++ b/Source/JavaScriptCore/DerivedSources.make
>@@ -48,7 +48,6 @@ all : \
>     JSPromiseConstructor.lut.h \
>     KeywordLookup.h \
>     Lexer.lut.h \
>-    NamePrototype.lut.h \
>     NumberConstructor.lut.h \
>     NumberPrototype.lut.h \
>     ObjectConstructor.lut.h \
>@@ -57,6 +56,7 @@ all : \
>     RegExpJitTables.h \
>     RegExpObject.lut.h \
>     StringConstructor.lut.h \
>+    SymbolPrototype.lut.h \
>     udis86_itab.h \
>     Bytecodes.h \
>     InitBytecodes.asm \
>diff --git a/Source/JavaScriptCore/JavaScriptCore.order b/Source/JavaScriptCore/JavaScriptCore.order
>index fd684f6f0039c5929d0b133a3057bac3cc916c0b..26be0ee276e0ee5c86e610999f2d476b0dd806de 100644
>--- a/Source/JavaScriptCore/JavaScriptCore.order
>+++ b/Source/JavaScriptCore/JavaScriptCore.order
>@@ -4599,14 +4599,8 @@ __ZN3JSCL24regExpConstructorDollar6EPNS_9ExecStateENS_7JSValueENS_12PropertyName
> __ZN3JSC5LexerIhE23parseIdentifierSlowCaseILb1EEENS_11JSTokenTypeEPNS_11JSTokenDataEjb
> __ZN3JSC4Yarr13YarrGeneratorILNS0_18YarrJITCompileModeE1EE33generatePatternCharacterNonGreedyEm
> __ZN3JSC4Yarr13YarrGeneratorILNS0_18YarrJITCompileModeE1EE34backtrackPatternCharacterNonGreedyEm
>-__ZN3JSC13NamePrototypeC1EPNS_9ExecStateEPNS_9StructureE
>-__ZN3JSC12NameInstanceC2ERNS_2VMEPNS_9StructureEPNS_8JSStringE
>-__ZN3JSC13NamePrototype14finishCreationEPNS_9ExecStateE
>-__ZN3JSC15NameConstructorC1EPNS_14JSGlobalObjectEPNS_9StructureE
>-__ZN3JSC15NameConstructor14finishCreationEPNS_9ExecStateEPNS_13NamePrototypeE
> _JSStringIsEqualToUTF8CString
> _JSStringIsEqual
>-__ZN3JSC12NameInstance7destroyEPNS_6JSCellE
> __ZN3WTF3MD5C1Ev
> __ZN3WTF3MD58addBytesEPKhm
> __ZN3WTFL12MD5TransformEPjPKj
>@@ -4756,9 +4750,7 @@ __ZN3JSC22createOutOfMemoryErrorEPNS_14JSGlobalObjectE
> __ZN3JSCL17mathProtoFuncACosEPNS_9ExecStateE
> __ZN3JSC11JSNameScope3putEPNS_6JSCellEPNS_9ExecStateENS_12PropertyNameENS_7JSValueERNS_15PutPropertySlotE
> __ZN3JSC14symbolTablePutINS_11JSNameScopeEEEbPT_PNS_9ExecStateENS_12PropertyNameENS_7JSValueEb
>-__ZN3JSC15NameConstructor11getCallDataEPNS_6JSCellERNS_8CallDataE
> __ZN3JSCL20constructPrivateNameEPNS_9ExecStateE
>-__ZN3JSC12NameInstanceC1ERNS_2VMEPNS_9StructureEPNS_8JSStringE
> __ZN3JSCL29objectProtoFuncToLocaleStringEPNS_9ExecStateE
> __ZN3JSC13JSNotAnObject24getOwnPropertyDescriptorEPNS_8JSObjectEPNS_9ExecStateENS_12PropertyNameERNS_18PropertyDescriptorE
> __ZN3JSCL20isNonLatin1IdentPartEi
>diff --git a/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj b/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj
>index f66eee61f6fc7ab554c974ec6ef3a948a6946176..86a7b38d5029687a53c1c20d853f4de0ddefb6d7 100644
>--- a/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj
>+++ b/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj
>@@ -773,9 +773,6 @@
>     <ClCompile Include="..\runtime\MapPrototype.cpp" />
>     <ClCompile Include="..\runtime\MathObject.cpp" />
>     <ClCompile Include="..\runtime\MemoryStatistics.cpp" />
>-    <ClCompile Include="..\runtime\NameConstructor.cpp" />
>-    <ClCompile Include="..\runtime\NameInstance.cpp" />
>-    <ClCompile Include="..\runtime\NamePrototype.cpp" />
>     <ClCompile Include="..\runtime\NativeErrorConstructor.cpp" />
>     <ClCompile Include="..\runtime\NativeErrorPrototype.cpp" />
>     <ClCompile Include="..\runtime\NullGetterFunction.cpp" />
>@@ -816,6 +813,10 @@
>     <ClCompile Include="..\runtime\StructureChain.cpp" />
>     <ClCompile Include="..\runtime\StructureIDTable.cpp" />
>     <ClCompile Include="..\runtime\StructureRareData.cpp" />
>+    <ClCompile Include="..\runtime\Symbol.cpp" />
>+    <ClCompile Include="..\runtime\SymbolConstructor.cpp" />
>+    <ClCompile Include="..\runtime\SymbolObject.cpp" />
>+    <ClCompile Include="..\runtime\SymbolPrototype.cpp" />
>     <ClCompile Include="..\runtime\SymbolTable.cpp" />
>     <ClCompile Include="..\runtime\TestRunnerUtils.cpp" />
>     <ClCompile Include="..\runtime\TypedArrayController.cpp" />
>@@ -863,7 +864,6 @@
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\JSPromisePrototype.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\KeywordLookup.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\Lexer.lut.h" />
>-    <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\NamePrototype.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\NumberConstructor.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\NumberPrototype.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\ObjectConstructor.lut.h" />
>@@ -872,6 +872,7 @@
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\RegExpObject.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\RegExpPrototype.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\StringConstructor.lut.h" />
>+    <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\SymbolPrototype.lut.h" />
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\JSCBuiltins.h" />
>   </ItemGroup>
>   <ItemGroup>
>@@ -1568,9 +1569,6 @@
>     <ClInclude Include="..\runtime\MathObject.h" />
>     <ClInclude Include="..\runtime\MemoryStatistics.h" />
>     <ClInclude Include="..\runtime\Microtask.h" />
>-    <ClInclude Include="..\runtime\NameConstructor.h" />
>-    <ClInclude Include="..\runtime\NameInstance.h" />
>-    <ClInclude Include="..\runtime\NamePrototype.h" />
>     <ClInclude Include="..\runtime\NativeErrorConstructor.h" />
>     <ClInclude Include="..\runtime\NativeErrorPrototype.h" />
>     <ClInclude Include="..\runtime\NullGetterFunction.h" />
>@@ -1625,6 +1623,10 @@
>     <ClInclude Include="..\runtime\StructureRareData.h" />
>     <ClInclude Include="..\runtime\StructureRareDataInlines.h" />
>     <ClInclude Include="..\runtime\StructureTransitionTable.h" />
>+    <ClInclude Include="..\runtime\Symbol.h" />
>+    <ClInclude Include="..\runtime\SymbolConstructor.h" />
>+    <ClInclude Include="..\runtime\SymbolObject.h" />
>+    <ClInclude Include="..\runtime\SymbolPrototype.h" />
>     <ClInclude Include="..\runtime\SymbolTable.h" />
>     <ClInclude Include="..\runtime\TestRunnerUtils.h" />
>     <ClInclude Include="..\runtime\Tracing.h" />
>diff --git a/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters b/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters
>index 515a32c7e50b2122e60e11cded4d97c595164780..ac530651067b208d79ed5ba8b678737096e9456d 100644
>--- a/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters
>+++ b/Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj.filters
>@@ -741,15 +741,6 @@
>     <ClCompile Include="..\runtime\MathObject.cpp">
>       <Filter>runtime</Filter>
>     </ClCompile>
>-    <ClCompile Include="..\runtime\NameConstructor.cpp">
>-      <Filter>runtime</Filter>
>-    </ClCompile>
>-    <ClCompile Include="..\runtime\NameInstance.cpp">
>-      <Filter>runtime</Filter>
>-    </ClCompile>
>-    <ClCompile Include="..\runtime\NamePrototype.cpp">
>-      <Filter>runtime</Filter>
>-    </ClCompile>
>     <ClCompile Include="..\runtime\NativeErrorConstructor.cpp">
>       <Filter>runtime</Filter>
>     </ClCompile>
>@@ -861,6 +852,18 @@
>     <ClCompile Include="..\runtime\StructureIDTable.cpp">
>       <Filter>runtime</Filter>
>     </ClCompile>
>+    <ClCompile Include="..\runtime\Symbol.cpp">
>+      <Filter>runtime</Filter>
>+    </ClInclude>
>+    <ClCompile Include="..\runtime\SymbolConstructor.cpp">
>+      <Filter>runtime</Filter>
>+    </ClCompile>
>+    <ClCompile Include="..\runtime\SymbolObject.cpp">
>+      <Filter>runtime</Filter>
>+    </ClCompile>
>+    <ClCompile Include="..\runtime\SymbolPrototype.cpp">
>+      <Filter>runtime</Filter>
>+    </ClCompile>
>     <ClCompile Include="..\runtime\SymbolTable.cpp">
>       <Filter>runtime</Filter>
>     </ClCompile>
>@@ -2759,15 +2762,6 @@
>     <ClInclude Include="..\runtime\MathObject.h">
>       <Filter>runtime</Filter>
>     </ClInclude>
>-    <ClInclude Include="..\runtime\NameConstructor.h">
>-      <Filter>runtime</Filter>
>-    </ClInclude>
>-    <ClInclude Include="..\runtime\NameInstance.h">
>-      <Filter>runtime</Filter>
>-    </ClInclude>
>-    <ClInclude Include="..\runtime\NamePrototype.h">
>-      <Filter>runtime</Filter>
>-    </ClInclude>
>     <ClInclude Include="..\runtime\NativeErrorConstructor.h">
>       <Filter>runtime</Filter>
>     </ClInclude>
>@@ -2903,6 +2897,18 @@
>     <ClInclude Include="..\runtime\StructureTransitionTable.h">
>       <Filter>runtime</Filter>
>     </ClInclude>
>+    <ClInclude Include="..\runtime\Symbol.h">
>+      <Filter>runtime</Filter>
>+    </ClInclude>
>+    <ClInclude Include="..\runtime\SymbolConstructor.h">
>+      <Filter>runtime</Filter>
>+    </ClInclude>
>+    <ClInclude Include="..\runtime\SymbolObject.h">
>+      <Filter>runtime</Filter>
>+    </ClInclude>
>+    <ClInclude Include="..\runtime\SymbolPrototype.h">
>+      <Filter>runtime</Filter>
>+    </ClInclude>
>     <ClInclude Include="..\runtime\SymbolTable.h">
>       <Filter>runtime</Filter>
>     </ClInclude>
>@@ -3249,7 +3255,7 @@
>     <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\RegExpObject.lut.h">
>       <Filter>Derived Sources</Filter>
>     </ClInclude>
>-    <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\NamePrototype.lut.h">
>+    <ClInclude Include="$(ConfigurationBuildDir)\obj$(PlatformArchitecture)\$(ProjectName)\DerivedSources\SymbolPrototype.lut.h">
>       <Filter>Derived Sources</Filter>
>     </ClInclude>
>     <ClInclude Include="..\heap\CodeBlockSet.h">
>diff --git a/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj b/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
>index 4ffe6a0f26e26f73de16d47392cf4c383ad542a1..9667ceb35282fa96d4fba1d136b73598bb5918df 100644
>--- a/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
>+++ b/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
>@@ -930,6 +930,14 @@
> 		65C0285D1717966800351E35 /* ARMv7DOpcode.h in Headers */ = {isa = PBXBuildFile; fileRef = 65C0285B1717966800351E35 /* ARMv7DOpcode.h */; };
> 		65FB5117184EEE7000C12B70 /* ProtoCallFrame.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 65FB5116184EE9BC00C12B70 /* ProtoCallFrame.cpp */; };
> 		6AD2CB4D19B9140100065719 /* DebuggerEvalEnabler.h in Headers */ = {isa = PBXBuildFile; fileRef = 6AD2CB4C19B9140100065719 /* DebuggerEvalEnabler.h */; settings = {ATTRIBUTES = (Private, ); }; };
>+		705B41AB1A6E501E00716757 /* Symbol.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 705B41A31A6E501E00716757 /* Symbol.cpp */; };
>+		705B41AC1A6E501E00716757 /* Symbol.h in Headers */ = {isa = PBXBuildFile; fileRef = 705B41A41A6E501E00716757 /* Symbol.h */; settings = {ATTRIBUTES = (Private, ); }; };
>+		705B41AD1A6E501E00716757 /* SymbolConstructor.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 705B41A51A6E501E00716757 /* SymbolConstructor.cpp */; };
>+		705B41AE1A6E501E00716757 /* SymbolConstructor.h in Headers */ = {isa = PBXBuildFile; fileRef = 705B41A61A6E501E00716757 /* SymbolConstructor.h */; settings = {ATTRIBUTES = (Private, ); }; };
>+		705B41AF1A6E501E00716757 /* SymbolObject.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 705B41A71A6E501E00716757 /* SymbolObject.cpp */; };
>+		705B41B01A6E501E00716757 /* SymbolObject.h in Headers */ = {isa = PBXBuildFile; fileRef = 705B41A81A6E501E00716757 /* SymbolObject.h */; settings = {ATTRIBUTES = (Private, ); }; };
>+		705B41B11A6E501E00716757 /* SymbolPrototype.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 705B41A91A6E501E00716757 /* SymbolPrototype.cpp */; };
>+		705B41B21A6E501E00716757 /* SymbolPrototype.h in Headers */ = {isa = PBXBuildFile; fileRef = 705B41AA1A6E501E00716757 /* SymbolPrototype.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		7C008CD2186F8A9300955C24 /* JSPromiseFunctions.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 7C008CD0186F8A9300955C24 /* JSPromiseFunctions.cpp */; };
> 		7C008CD3186F8A9300955C24 /* JSPromiseFunctions.h in Headers */ = {isa = PBXBuildFile; fileRef = 7C008CD1186F8A9300955C24 /* JSPromiseFunctions.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		7C008CDA187124BB00955C24 /* JSPromiseDeferred.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 7C008CD8187124BB00955C24 /* JSPromiseDeferred.cpp */; };
>@@ -1015,12 +1023,6 @@
> 		86E3C61C167BABEE006D760A /* JSVirtualMachine.mm in Sources */ = {isa = PBXBuildFile; fileRef = 86E3C610167BAB87006D760A /* JSVirtualMachine.mm */; };
> 		86E3C61D167BABEE006D760A /* JSVirtualMachineInternal.h in Headers */ = {isa = PBXBuildFile; fileRef = 86E3C611167BAB87006D760A /* JSVirtualMachineInternal.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		86E85539111B9968001AF51E /* JSStringBuilder.h in Headers */ = {isa = PBXBuildFile; fileRef = 86E85538111B9968001AF51E /* JSStringBuilder.h */; };
>-		86EBF2FF1560F06A008E9222 /* NameConstructor.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86EBF2F91560F036008E9222 /* NameConstructor.cpp */; };
>-		86EBF3001560F06A008E9222 /* NameConstructor.h in Headers */ = {isa = PBXBuildFile; fileRef = 86EBF2FA1560F036008E9222 /* NameConstructor.h */; };
>-		86EBF3011560F06A008E9222 /* NameInstance.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86EBF2FB1560F036008E9222 /* NameInstance.cpp */; };
>-		86EBF3021560F06A008E9222 /* NameInstance.h in Headers */ = {isa = PBXBuildFile; fileRef = 86EBF2FC1560F036008E9222 /* NameInstance.h */; };
>-		86EBF3031560F06A008E9222 /* NamePrototype.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86EBF2FD1560F036008E9222 /* NamePrototype.cpp */; };
>-		86EBF3041560F06A008E9222 /* NamePrototype.h in Headers */ = {isa = PBXBuildFile; fileRef = 86EBF2FE1560F036008E9222 /* NamePrototype.h */; };
> 		86EC9DC41328DF82002B2AD7 /* DFGByteCodeParser.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86EC9DB41328DF82002B2AD7 /* DFGByteCodeParser.cpp */; };
> 		86EC9DC51328DF82002B2AD7 /* DFGByteCodeParser.h in Headers */ = {isa = PBXBuildFile; fileRef = 86EC9DB51328DF82002B2AD7 /* DFGByteCodeParser.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		86EC9DC61328DF82002B2AD7 /* DFGGenerationInfo.h in Headers */ = {isa = PBXBuildFile; fileRef = 86EC9DB61328DF82002B2AD7 /* DFGGenerationInfo.h */; settings = {ATTRIBUTES = (Private, ); }; };
>@@ -2597,6 +2599,14 @@
> 		65FB5116184EE9BC00C12B70 /* ProtoCallFrame.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = ProtoCallFrame.cpp; sourceTree = "<group>"; };
> 		6AD2CB4C19B9140100065719 /* DebuggerEvalEnabler.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = DebuggerEvalEnabler.h; sourceTree = "<group>"; };
> 		704FD35305697E6D003DBED9 /* BooleanObject.h */ = {isa = PBXFileReference; fileEncoding = 30; indentWidth = 4; lastKnownFileType = sourcecode.c.h; path = BooleanObject.h; sourceTree = "<group>"; tabWidth = 8; };
>+		705B41A31A6E501E00716757 /* Symbol.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Symbol.cpp; sourceTree = "<group>"; };
>+		705B41A41A6E501E00716757 /* Symbol.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = Symbol.h; sourceTree = "<group>"; };
>+		705B41A51A6E501E00716757 /* SymbolConstructor.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SymbolConstructor.cpp; sourceTree = "<group>"; };
>+		705B41A61A6E501E00716757 /* SymbolConstructor.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SymbolConstructor.h; sourceTree = "<group>"; };
>+		705B41A71A6E501E00716757 /* SymbolObject.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SymbolObject.cpp; sourceTree = "<group>"; };
>+		705B41A81A6E501E00716757 /* SymbolObject.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SymbolObject.h; sourceTree = "<group>"; };
>+		705B41A91A6E501E00716757 /* SymbolPrototype.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SymbolPrototype.cpp; sourceTree = "<group>"; };
>+		705B41AA1A6E501E00716757 /* SymbolPrototype.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SymbolPrototype.h; sourceTree = "<group>"; };
> 		7C008CD0186F8A9300955C24 /* JSPromiseFunctions.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; lineEnding = 0; path = JSPromiseFunctions.cpp; sourceTree = "<group>"; xcLanguageSpecificationIdentifier = xcode.lang.cpp; };
> 		7C008CD1186F8A9300955C24 /* JSPromiseFunctions.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = JSPromiseFunctions.h; sourceTree = "<group>"; };
> 		7C008CD8187124BB00955C24 /* JSPromiseDeferred.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = JSPromiseDeferred.cpp; sourceTree = "<group>"; };
>@@ -2694,12 +2704,6 @@
> 		86E3C610167BAB87006D760A /* JSVirtualMachine.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = JSVirtualMachine.mm; sourceTree = "<group>"; };
> 		86E3C611167BAB87006D760A /* JSVirtualMachineInternal.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = JSVirtualMachineInternal.h; sourceTree = "<group>"; };
> 		86E85538111B9968001AF51E /* JSStringBuilder.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = JSStringBuilder.h; sourceTree = "<group>"; };
>-		86EBF2F91560F036008E9222 /* NameConstructor.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = NameConstructor.cpp; sourceTree = "<group>"; };
>-		86EBF2FA1560F036008E9222 /* NameConstructor.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = NameConstructor.h; sourceTree = "<group>"; };
>-		86EBF2FB1560F036008E9222 /* NameInstance.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = NameInstance.cpp; sourceTree = "<group>"; };
>-		86EBF2FC1560F036008E9222 /* NameInstance.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = NameInstance.h; sourceTree = "<group>"; };
>-		86EBF2FD1560F036008E9222 /* NamePrototype.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = NamePrototype.cpp; sourceTree = "<group>"; };
>-		86EBF2FE1560F036008E9222 /* NamePrototype.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = NamePrototype.h; sourceTree = "<group>"; };
> 		86EC9DB41328DF82002B2AD7 /* DFGByteCodeParser.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = DFGByteCodeParser.cpp; path = dfg/DFGByteCodeParser.cpp; sourceTree = "<group>"; };
> 		86EC9DB51328DF82002B2AD7 /* DFGByteCodeParser.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = DFGByteCodeParser.h; path = dfg/DFGByteCodeParser.h; sourceTree = "<group>"; };
> 		86EC9DB61328DF82002B2AD7 /* DFGGenerationInfo.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = DFGGenerationInfo.h; path = dfg/DFGGenerationInfo.h; sourceTree = "<group>"; };
>@@ -4438,12 +4442,6 @@
> 				90213E3B123A40C200D422F3 /* MemoryStatistics.cpp */,
> 				90213E3C123A40C200D422F3 /* MemoryStatistics.h */,
> 				7C008CE5187631B600955C24 /* Microtask.h */,
>-				86EBF2F91560F036008E9222 /* NameConstructor.cpp */,
>-				86EBF2FA1560F036008E9222 /* NameConstructor.h */,
>-				86EBF2FB1560F036008E9222 /* NameInstance.cpp */,
>-				86EBF2FC1560F036008E9222 /* NameInstance.h */,
>-				86EBF2FD1560F036008E9222 /* NamePrototype.cpp */,
>-				86EBF2FE1560F036008E9222 /* NamePrototype.h */,
> 				BC02E9080E1839DB000F9297 /* NativeErrorConstructor.cpp */,
> 				BC02E9090E1839DB000F9297 /* NativeErrorConstructor.h */,
> 				BC02E90A0E1839DB000F9297 /* NativeErrorPrototype.cpp */,
>@@ -4541,6 +4539,14 @@
> 				C2FE18A316BAEC4000AF3061 /* StructureRareData.h */,
> 				C20BA92C16BB1C1500B3AEA2 /* StructureRareDataInlines.h */,
> 				BC9041470EB9250900FE26FA /* StructureTransitionTable.h */,
>+				705B41A31A6E501E00716757 /* Symbol.cpp */,
>+				705B41A41A6E501E00716757 /* Symbol.h */,
>+				705B41A51A6E501E00716757 /* SymbolConstructor.cpp */,
>+				705B41A61A6E501E00716757 /* SymbolConstructor.h */,
>+				705B41A71A6E501E00716757 /* SymbolObject.cpp */,
>+				705B41A81A6E501E00716757 /* SymbolObject.h */,
>+				705B41A91A6E501E00716757 /* SymbolPrototype.cpp */,
>+				705B41AA1A6E501E00716757 /* SymbolPrototype.h */,
> 				0F919D2715856770004A4E7D /* SymbolTable.cpp */,
> 				14A396A60CD2933100B5B4FF /* SymbolTable.h */,
> 				0FA2C17917D7CF84009D015F /* TestRunnerUtils.cpp */,
>@@ -6053,9 +6059,6 @@
> 				0F3D0BBD194A414300FC9CF9 /* ConstantStructureCheck.h in Headers */,
> 				7C008CE7187631B600955C24 /* Microtask.h in Headers */,
> 				86C568E211A213EE0007F7F0 /* MIPSAssembler.h in Headers */,
>-				86EBF3001560F06A008E9222 /* NameConstructor.h in Headers */,
>-				86EBF3021560F06A008E9222 /* NameInstance.h in Headers */,
>-				86EBF3041560F06A008E9222 /* NamePrototype.h in Headers */,
> 				BC02E9110E1839DB000F9297 /* NativeErrorConstructor.h in Headers */,
> 				BC02E9130E1839DB000F9297 /* NativeErrorPrototype.h in Headers */,
> 				99CC0B6318BE9950006CEBCC /* CodeGeneratorReplayInputs.py in Headers */,
>@@ -6214,6 +6217,10 @@
> 				BCCF0D080EF0AAB900413C8F /* StructureStubInfo.h in Headers */,
> 				BC9041480EB9250900FE26FA /* StructureTransitionTable.h in Headers */,
> 				C2DF44301707AC0100A5CA96 /* SuperRegion.h in Headers */,
>+				705B41AC1A6E501E00716757 /* Symbol.h in Headers */,
>+				705B41AE1A6E501E00716757 /* SymbolConstructor.h in Headers */,
>+				705B41B01A6E501E00716757 /* SymbolObject.h in Headers */,
>+				705B41B21A6E501E00716757 /* SymbolPrototype.h in Headers */,
> 				BC18C46B0E16F5CD00B34460 /* SymbolTable.h in Headers */,
> 				A784A26411D16622005776AC /* SyntaxChecker.h in Headers */,
> 				0F24E54F17EE274900ABB217 /* TempRegisterSet.h in Headers */,
>@@ -7180,9 +7187,6 @@
> 				14469DDF107EC7E700650446 /* MathObject.cpp in Sources */,
> 				90213E3D123A40C200D422F3 /* MemoryStatistics.cpp in Sources */,
> 				0FB5467D14F5CFD6002C2989 /* MethodOfGettingAValueProfile.cpp in Sources */,
>-				86EBF2FF1560F06A008E9222 /* NameConstructor.cpp in Sources */,
>-				86EBF3011560F06A008E9222 /* NameInstance.cpp in Sources */,
>-				86EBF3031560F06A008E9222 /* NamePrototype.cpp in Sources */,
> 				14469DE0107EC7E700650446 /* NativeErrorConstructor.cpp in Sources */,
> 				14469DE1107EC7E700650446 /* NativeErrorPrototype.cpp in Sources */,
> 				148F21B7107EC5470042EC2C /* Nodes.cpp in Sources */,
>@@ -7283,6 +7287,10 @@
> 				0F766D3815AE4A1C008F363E /* StructureStubClearingWatchpoint.cpp in Sources */,
> 				BCCF0D0C0EF0B8A500413C8F /* StructureStubInfo.cpp in Sources */,
> 				C2DF442F1707AC0100A5CA96 /* SuperRegion.cpp in Sources */,
>+				705B41AB1A6E501E00716757 /* Symbol.cpp in Sources */,
>+				705B41AD1A6E501E00716757 /* SymbolConstructor.cpp in Sources */,
>+				705B41AF1A6E501E00716757 /* SymbolObject.cpp in Sources */,
>+				705B41B11A6E501E00716757 /* SymbolPrototype.cpp in Sources */,
> 				0F919D2815856773004A4E7D /* SymbolTable.cpp in Sources */,
> 				0FC314131814559100033232 /* TempRegisterSet.cpp in Sources */,
> 				0FA2C17B17D7CF84009D015F /* TestRunnerUtils.cpp in Sources */,
>diff --git a/Source/JavaScriptCore/builtins/BuiltinExecutables.cpp b/Source/JavaScriptCore/builtins/BuiltinExecutables.cpp
>index ef6737ee2c7e775bffd056a512dc3c23b0e885ed..9fcdaa1e38dc6575bb791399a8e3aadc01913328 100644
>--- a/Source/JavaScriptCore/builtins/BuiltinExecutables.cpp
>+++ b/Source/JavaScriptCore/builtins/BuiltinExecutables.cpp
>@@ -75,7 +75,7 @@ UnlinkedFunctionExecutable* BuiltinExecutables::createBuiltinExecutable(const So
>         
>         if (closedVariable == m_vm.propertyNames->undefinedKeyword.impl())
>             continue;
>-        RELEASE_ASSERT(closedVariable->isEmptyUnique());
>+        RELEASE_ASSERT(closedVariable->isUnique());
>     }
>     body->overrideName(name);
>     UnlinkedFunctionExecutable* functionExecutable = UnlinkedFunctionExecutable::create(&m_vm, source, body, UnlinkedBuiltinFunction);
>diff --git a/Source/JavaScriptCore/builtins/BuiltinNames.h b/Source/JavaScriptCore/builtins/BuiltinNames.h
>index 67e1f563bca018d03209cf81052623601ba4405b..9b8896b968014913f46b32c480e057896379dfa4 100644
>--- a/Source/JavaScriptCore/builtins/BuiltinNames.h
>+++ b/Source/JavaScriptCore/builtins/BuiltinNames.h
>@@ -31,7 +31,7 @@
> 
> namespace JSC {
>     
>-#define INITIALISE_BUILTIN_NAMES(name) , m_##name(vm, #name), m_##name##PrivateName(Identifier::from(PrivateName()))
>+#define INITIALISE_BUILTIN_NAMES(name) , m_##name(vm, #name), m_##name##PrivateName(Identifier::from(PrivateName(ASCIILiteral("Symbol." #name))))
> #define DECLARE_BUILTIN_NAMES(name) const Identifier m_##name; const Identifier m_##name##PrivateName;;
> #define DECLARE_BUILTIN_IDENTIFIER_ACCESSOR(name) \
>     const Identifier& name##PublicName() const { return m_##name; } \
>diff --git a/Source/JavaScriptCore/dfg/DFGOperations.cpp b/Source/JavaScriptCore/dfg/DFGOperations.cpp
>index 795e60583526c37603c31872877522b8fd8b7892..92e9cc219067ea42916f1454b15e4ba0ce3a4da2 100644
>--- a/Source/JavaScriptCore/dfg/DFGOperations.cpp
>+++ b/Source/JavaScriptCore/dfg/DFGOperations.cpp
>@@ -48,11 +48,11 @@
> #include "JSLexicalEnvironment.h"
> #include "VM.h"
> #include "JSNameScope.h"
>-#include "NameInstance.h"
> #include "ObjectConstructor.h"
> #include "JSCInlines.h"
> #include "Repatch.h"
> #include "StringConstructor.h"
>+#include "Symbol.h"
> #include "TypeProfilerLog.h"
> #include "TypedArrayInlines.h"
> #include <wtf/InlineASM.h>
>@@ -110,25 +110,15 @@ ALWAYS_INLINE static void JIT_OPERATION operationPutByValInternal(ExecState* exe
>         }
>     }
> 
>-    if (isName(property)) {
>-        PutPropertySlot slot(baseValue, strict);
>-        if (direct) {
>-            RELEASE_ASSERT(baseValue.isObject());
>-            asObject(baseValue)->putDirect(*vm, jsCast<NameInstance*>(property.asCell())->privateName(), value, slot);
>-        } else
>-            baseValue.put(exec, jsCast<NameInstance*>(property.asCell())->privateName(), value, slot);
>-        return;
>-    }
>-
>     // Don't put to an object if toString throws an exception.
>-    Identifier ident = property.toString(exec)->toIdentifier(exec);
>+    PropertyName propertyName = property.toPropertyKey(exec);
>     if (!vm->exception()) {
>         PutPropertySlot slot(baseValue, strict);
>         if (direct) {
>             RELEASE_ASSERT(baseValue.isObject());
>-            asObject(baseValue)->putDirect(*vm, ident, value, slot);
>+            asObject(baseValue)->putDirect(*vm, propertyName, value, slot);
>         } else
>-            baseValue.put(exec, ident, value, slot);
>+            baseValue.put(exec, propertyName, value, slot);
>     }
> }
> 
>@@ -306,11 +296,8 @@ EncodedJSValue JIT_OPERATION operationGetByVal(ExecState* exec, EncodedJSValue e
>         }
>     }
> 
>-    if (isName(property))
>-        return JSValue::encode(baseValue.get(exec, jsCast<NameInstance*>(property.asCell())->privateName()));
>-
>-    Identifier ident = property.toString(exec)->toIdentifier(exec);
>-    return JSValue::encode(baseValue.get(exec, ident));
>+    PropertyName propertyName = property.toPropertyKey(exec);
>+    return JSValue::encode(baseValue.get(exec, propertyName));
> }
> 
> EncodedJSValue JIT_OPERATION operationGetByValCell(ExecState* exec, JSCell* base, EncodedJSValue encodedProperty)
>@@ -337,11 +324,8 @@ EncodedJSValue JIT_OPERATION operationGetByValCell(ExecState* exec, JSCell* base
>         }
>     }
> 
>-    if (isName(property))
>-        return JSValue::encode(JSValue(base).get(exec, jsCast<NameInstance*>(property.asCell())->privateName()));
>-
>-    Identifier ident = property.toString(exec)->toIdentifier(exec);
>-    return JSValue::encode(JSValue(base).get(exec, ident));
>+    PropertyName propertyName = property.toPropertyKey(exec);
>+    return JSValue::encode(JSValue(base).get(exec, propertyName));
> }
> 
> ALWAYS_INLINE EncodedJSValue getByValCellInt(ExecState* exec, JSCell* base, int32_t index)
>diff --git a/Source/JavaScriptCore/interpreter/Interpreter.cpp b/Source/JavaScriptCore/interpreter/Interpreter.cpp
>index d11a4816b765e9daa370a050f471f137346c46a4..ebe2402e5084f009c502f4b4416d5cc58159d82e 100644
>--- a/Source/JavaScriptCore/interpreter/Interpreter.cpp
>+++ b/Source/JavaScriptCore/interpreter/Interpreter.cpp
>@@ -54,7 +54,6 @@
> #include "LLIntThunks.h"
> #include "LegacyProfiler.h"
> #include "LiteralParser.h"
>-#include "NameInstance.h"
> #include "ObjectPrototype.h"
> #include "JSCInlines.h"
> #include "Parser.h"
>@@ -67,6 +66,7 @@
> #include "StackVisitor.h"
> #include "StrictEvalActivation.h"
> #include "StrongInlines.h"
>+#include "Symbol.h"
> #include "VMEntryScope.h"
> #include "VirtualRegister.h"
> 
>diff --git a/Source/JavaScriptCore/jit/JITOperations.cpp b/Source/JavaScriptCore/jit/JITOperations.cpp
>index 37aa45d5363911a5963f0c90c0d1cedfbbe322dd..3885c06a0f5cba9ddecab52846c576150365d067 100644
>--- a/Source/JavaScriptCore/jit/JITOperations.cpp
>+++ b/Source/JavaScriptCore/jit/JITOperations.cpp
>@@ -159,7 +159,7 @@ EncodedJSValue JIT_OPERATION operationGetByIdOptimize(ExecState* exec, Structure
> {
>     VM* vm = &exec->vm();
>     NativeCallFrameTracer tracer(vm, exec);
>-    Identifier ident = uid->isEmptyUnique() ? Identifier::from(PrivateName(uid)) : Identifier(vm, uid);
>+    Identifier ident = uid->isUnique() ? Identifier::from(PrivateName(uid)) : Identifier(vm, uid);
> 
>     JSValue baseValue = JSValue::decode(base);
>     PropertySlot slot(baseValue);
>@@ -466,11 +466,8 @@ static void putByVal(CallFrame* callFrame, JSValue baseValue, JSValue subscript,
>                 object->methodTable(vm)->putByIndex(object, callFrame, i, value, callFrame->codeBlock()->isStrictMode());
>         } else
>             baseValue.putByIndex(callFrame, i, value, callFrame->codeBlock()->isStrictMode());
>-    } else if (isName(subscript)) {
>-        PutPropertySlot slot(baseValue, callFrame->codeBlock()->isStrictMode());
>-        baseValue.put(callFrame, jsCast<NameInstance*>(subscript.asCell())->privateName(), value, slot);
>     } else {
>-        Identifier property = subscript.toString(callFrame)->toIdentifier(callFrame);
>+        PropertyName property = subscript.toPropertyKey(callFrame);
>         if (!callFrame->vm().exception()) { // Don't put to an object if toString threw an exception.
>             PutPropertySlot slot(baseValue, callFrame->codeBlock()->isStrictMode());
>             baseValue.put(callFrame, property, value, slot);
>@@ -483,11 +480,8 @@ static void directPutByVal(CallFrame* callFrame, JSObject* baseObject, JSValue s
>     if (LIKELY(subscript.isUInt32())) {
>         uint32_t i = subscript.asUInt32();
>         baseObject->putDirectIndex(callFrame, i, value);
>-    } else if (isName(subscript)) {
>-        PutPropertySlot slot(baseObject, callFrame->codeBlock()->isStrictMode());
>-        baseObject->putDirect(callFrame->vm(), jsCast<NameInstance*>(subscript.asCell())->privateName(), value, slot);
>     } else {
>-        Identifier property = subscript.toString(callFrame)->toIdentifier(callFrame);
>+        PropertyName property = subscript.toPropertyKey(callFrame);
>         if (!callFrame->vm().exception()) { // Don't put to an object if toString threw an exception.
>             PutPropertySlot slot(baseObject, callFrame->codeBlock()->isStrictMode());
>             baseObject->putDirect(callFrame->vm(), property, value, slot);
>@@ -1467,10 +1461,7 @@ static JSValue getByVal(ExecState* exec, JSValue baseValue, JSValue subscript, R
>         return baseValue.get(exec, i);
>     }
> 
>-    if (isName(subscript))
>-        return baseValue.get(exec, jsCast<NameInstance*>(subscript.asCell())->privateName());
>-
>-    Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+    PropertyName property = subscript.toPropertyKey(exec);
>     return baseValue.get(exec, property);
> }
> 
>@@ -1605,10 +1596,8 @@ EncodedJSValue JIT_OPERATION operationGetByValString(ExecState* exec, EncodedJSV
>             if (!isJSString(baseValue))
>                 ctiPatchCallByReturnAddress(exec->codeBlock(), ReturnAddressPtr(OUR_RETURN_ADDRESS), FunctionPtr(operationGetByValDefault));
>         }
>-    } else if (isName(subscript))
>-        result = baseValue.get(exec, jsCast<NameInstance*>(subscript.asCell())->privateName());
>-    else {
>-        Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+    } else {
>+        PropertyName property = subscript.toPropertyKey(exec);
>         result = baseValue.get(exec, property);
>     }
> 
>diff --git a/Source/JavaScriptCore/llint/LLIntData.cpp b/Source/JavaScriptCore/llint/LLIntData.cpp
>index 997e3b98ff97f8684d07a117b7714fb10e96f541..ab01501b12917d9ee80ed31523f9258dc442da2e 100644
>--- a/Source/JavaScriptCore/llint/LLIntData.cpp
>+++ b/Source/JavaScriptCore/llint/LLIntData.cpp
>@@ -132,8 +132,8 @@ void Data::performAssertions(VM& vm)
>     ASSERT(maxFrameExtentForSlowPathCall == 64);
> #endif
>     ASSERT(StringType == 6);
>-    ASSERT(ObjectType == 17);
>-    ASSERT(FinalObjectType == 18);
>+    ASSERT(ObjectType == 18);
>+    ASSERT(FinalObjectType == 19);
>     ASSERT(MasqueradesAsUndefined == 1);
>     ASSERT(ImplementsHasInstance == 2);
>     ASSERT(ImplementsDefaultHasInstance == 8);
>diff --git a/Source/JavaScriptCore/llint/LLIntSlowPaths.cpp b/Source/JavaScriptCore/llint/LLIntSlowPaths.cpp
>index 85bac2603a7b2157b9559b2fe185a677652d2d5e..a3022cba19d916d0f0849307a7b72d83c9cdde3e 100644
>--- a/Source/JavaScriptCore/llint/LLIntSlowPaths.cpp
>+++ b/Source/JavaScriptCore/llint/LLIntSlowPaths.cpp
>@@ -744,10 +744,7 @@ inline JSValue getByVal(ExecState* exec, JSValue baseValue, JSValue subscript)
>         return baseValue.get(exec, i);
>     }
> 
>-    if (isName(subscript))
>-        return baseValue.get(exec, jsCast<NameInstance*>(subscript.asCell())->privateName());
>-    
>-    Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+    PropertyName property = subscript.toPropertyKey(exec);
>     return baseValue.get(exec, property);
> }
> 
>@@ -797,13 +794,7 @@ inline JSValue getByVal(ExecState* exec, JSValue baseValue, JSValue subscript)
>         LLINT_END();
>     }
> 
>-    if (isName(subscript)) {
>-        PutPropertySlot slot(baseValue, exec->codeBlock()->isStrictMode());
>-        baseValue.put(exec, jsCast<NameInstance*>(subscript.asCell())->privateName(), value, slot);
>-        LLINT_END();
>-    }
>-
>-    Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+    PropertyName property = subscript.toPropertyKey(exec);
>     LLINT_CHECK_EXCEPTION();
>     PutPropertySlot slot(baseValue, exec->codeBlock()->isStrictMode());
>     baseValue.put(exec, property, value, slot);
>@@ -822,11 +813,8 @@ inline JSValue getByVal(ExecState* exec, JSValue baseValue, JSValue subscript)
>     if (LIKELY(subscript.isUInt32())) {
>         uint32_t i = subscript.asUInt32();
>         baseObject->putDirectIndex(exec, i, value);
>-    } else if (isName(subscript)) {
>-        PutPropertySlot slot(baseObject, exec->codeBlock()->isStrictMode());
>-        baseObject->putDirect(exec->vm(), jsCast<NameInstance*>(subscript.asCell())->privateName(), value, slot);
>     } else {
>-        Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+        PropertyName property = subscript.toPropertyKey(exec);
>         if (!exec->vm().exception()) { // Don't put to an object if toString threw an exception.
>             PutPropertySlot slot(baseObject, exec->codeBlock()->isStrictMode());
>             baseObject->putDirect(exec->vm(), property, value, slot);
>@@ -848,11 +836,9 @@ inline JSValue getByVal(ExecState* exec, JSValue baseValue, JSValue subscript)
>     uint32_t i;
>     if (subscript.getUInt32(i))
>         couldDelete = baseObject->methodTable()->deletePropertyByIndex(baseObject, exec, i);
>-    else if (isName(subscript))
>-        couldDelete = baseObject->methodTable()->deleteProperty(baseObject, exec, jsCast<NameInstance*>(subscript.asCell())->privateName());
>     else {
>         LLINT_CHECK_EXCEPTION();
>-        Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+        PropertyName property = subscript.toPropertyKey(exec);
>         LLINT_CHECK_EXCEPTION();
>         couldDelete = baseObject->methodTable()->deleteProperty(baseObject, exec, property);
>     }
>diff --git a/Source/JavaScriptCore/llint/LowLevelInterpreter.asm b/Source/JavaScriptCore/llint/LowLevelInterpreter.asm
>index f106d54acd3483b3d16648350d31a9f0236baeaa..043a00afbf8615682db9141957989fde8b1046a6 100644
>--- a/Source/JavaScriptCore/llint/LowLevelInterpreter.asm
>+++ b/Source/JavaScriptCore/llint/LowLevelInterpreter.asm
>@@ -153,8 +153,8 @@ const SlowPutArrayStorageShape = 30
> 
> # Type constants.
> const StringType = 6
>-const ObjectType = 17
>-const FinalObjectType = 18
>+const ObjectType = 18
>+const FinalObjectType = 19
> 
> # Type flags constants.
> const MasqueradesAsUndefined = 1
>diff --git a/Source/JavaScriptCore/runtime/CommonIdentifiers.h b/Source/JavaScriptCore/runtime/CommonIdentifiers.h
>index 569ee4ff38c9dbec8e4bae82a9ec58c9dc2c43b8..65815cc9a1e9f7c6210392203ac8f18107df8a70 100644
>--- a/Source/JavaScriptCore/runtime/CommonIdentifiers.h
>+++ b/Source/JavaScriptCore/runtime/CommonIdentifiers.h
>@@ -52,6 +52,7 @@
>     macro(Set)\
>     macro(SetIterator)\
>     macro(String) \
>+    macro(Symbol) \
>     macro(SyntaxError) \
>     macro(TypeError) \
>     macro(URIError) \
>@@ -219,8 +220,21 @@
>     macro(with) \
>     macro(yield)
> 
>-#define JSC_COMMON_PRIVATE_IDENTIFIERS_EACH_PROPERTY_NAME(macro) \
>+#define JSC_COMMON_PRIVATE_IDENTIFIERS_EACH_WELL_KNOWN_SYMBOL(macro) \
>+    macro(hasInstance) \
>+    macro(isConcatSpreadable) \
>     macro(iterator) \
>+    macro(match) \
>+    macro(replace) \
>+    macro(search) \
>+    macro(species) \
>+    macro(split) \
>+    macro(toPrimitive) \
>+    macro(toStringTag) \
>+    macro(unscopable)
>+
>+#define JSC_COMMON_PRIVATE_IDENTIFIERS_EACH_PROPERTY_NAME(macro) \
>+    JSC_COMMON_PRIVATE_IDENTIFIERS_EACH_WELL_KNOWN_SYMBOL(macro) \
>     macro(iteratorNext) \
>     macro(resolve) \
>     macro(reject) \
>diff --git a/Source/JavaScriptCore/runtime/CommonSlowPaths.cpp b/Source/JavaScriptCore/runtime/CommonSlowPaths.cpp
>index 08091a87e09d1f1ee98f4c0cc6b27bf50db15434..dfb94121690dc37e6015654bebad7404d1c363d7 100644
>--- a/Source/JavaScriptCore/runtime/CommonSlowPaths.cpp
>+++ b/Source/JavaScriptCore/runtime/CommonSlowPaths.cpp
>@@ -486,11 +486,9 @@ static CommonSlowPaths::ArityCheckData* setupArityCheckData(VM& vm, int slotsToA
>     uint32_t i;
>     if (subscript.getUInt32(i))
>         couldDelete = baseObject->methodTable()->deletePropertyByIndex(baseObject, exec, i);
>-    else if (isName(subscript))
>-        couldDelete = baseObject->methodTable()->deleteProperty(baseObject, exec, jsCast<NameInstance*>(subscript.asCell())->privateName());
>     else {
>         CHECK_EXCEPTION();
>-        Identifier property = subscript.toString(exec)->toIdentifier(exec);
>+        PropertyName property = subscript.toPropertyKey(exec);
>         CHECK_EXCEPTION();
>         couldDelete = baseObject->methodTable()->deleteProperty(baseObject, exec, property);
>     }
>@@ -575,7 +573,7 @@ static CommonSlowPaths::ArityCheckData* setupArityCheckData(VM& vm, int slotsToA
>     JSValue baseValue = OP_C(2).jsValue();
>     JSValue property = OP(3).jsValue();
>     ASSERT(property.isString());
>-    RETURN(baseValue.get(exec, property.toString(exec)->toIdentifier(exec)));
>+    RETURN(baseValue.get(exec, property.toPropertyKey(exec)));
> }
> 
> SLOW_PATH_DECL(slow_path_get_structure_property_enumerator)
>diff --git a/Source/JavaScriptCore/runtime/CommonSlowPaths.h b/Source/JavaScriptCore/runtime/CommonSlowPaths.h
>index a56358cd6e0977743e87b3c165e2cea1aa47eda6..bfe483df6f98bf15c7df506e14f27fafd36a75a6 100644
>--- a/Source/JavaScriptCore/runtime/CommonSlowPaths.h
>+++ b/Source/JavaScriptCore/runtime/CommonSlowPaths.h
>@@ -30,8 +30,8 @@
> #include "CodeSpecializationKind.h"
> #include "ExceptionHelpers.h"
> #include "JSStackInlines.h"
>-#include "NameInstance.h"
> #include "StackAlignment.h"
>+#include "Symbol.h"
> #include "VM.h"
> #include <wtf/StdLibExtras.h>
> 
>@@ -82,10 +82,7 @@ inline bool opIn(ExecState* exec, JSValue propName, JSValue baseVal)
>     if (propName.getUInt32(i))
>         return baseObj->hasProperty(exec, i);
> 
>-    if (isName(propName))
>-        return baseObj->hasProperty(exec, jsCast<NameInstance*>(propName.asCell())->privateName());
>-
>-    Identifier property = propName.toString(exec)->toIdentifier(exec);
>+    PropertyName property = propName.toPropertyKey(exec);
>     if (exec->vm().exception())
>         return false;
>     return baseObj->hasProperty(exec, property);
>diff --git a/Source/JavaScriptCore/runtime/ExceptionHelpers.cpp b/Source/JavaScriptCore/runtime/ExceptionHelpers.cpp
>index 5555395f32732582647bc9e57c62f0660da62ea3..105aaef7f09aae152b85f3208b14bbf90a1f5ac3 100644
>--- a/Source/JavaScriptCore/runtime/ExceptionHelpers.cpp
>+++ b/Source/JavaScriptCore/runtime/ExceptionHelpers.cpp
>@@ -82,7 +82,7 @@ JSObject* createStackOverflowError(JSGlobalObject* globalObject)
> JSObject* createUndefinedVariableError(ExecState* exec, const Identifier& ident)
> {
>     
>-    if (ident.impl()->isEmptyUnique()) {
>+    if (ident.impl()->isUnique()) {
>         String message(makeString("Can't find private variable: @", exec->propertyNames().getPublicName(ident).string()));
>         return createReferenceError(exec, message);
>     }
>diff --git a/Source/JavaScriptCore/runtime/JSCJSValue.cpp b/Source/JavaScriptCore/runtime/JSCJSValue.cpp
>index c233f4c70021cd78532859e15b0cb63076c9e95a..48756ba3b33f6cde8904e01f7f7b0934dd3e0ad7 100644
>--- a/Source/JavaScriptCore/runtime/JSCJSValue.cpp
>+++ b/Source/JavaScriptCore/runtime/JSCJSValue.cpp
>@@ -99,8 +99,10 @@ JSValue JSValue::toThisSlowCase(ExecState* exec, ECMAMode ecmaMode) const
> JSObject* JSValue::synthesizePrototype(ExecState* exec) const
> {
>     if (isCell()) {
>-        ASSERT(isString());
>-        return exec->lexicalGlobalObject()->stringPrototype();
>+        if (isString())
>+            return exec->lexicalGlobalObject()->stringPrototype();
>+        ASSERT(isSymbol());
>+        return exec->lexicalGlobalObject()->symbolPrototype();
>     }
> 
>     if (isNumber())
>@@ -231,7 +233,7 @@ void JSValue::dumpInContextAssumingStructure(
>                     out.print(" (atomic)");
>                 if (impl->isAtomic())
>                     out.print(" (identifier)");
>-                if (impl->isEmptyUnique())
>+                if (impl->isUnique())
>                     out.print(" (unique)");
>             } else
>                 out.print(" (unresolved)");
>@@ -364,6 +366,10 @@ JSString* JSValue::toStringSlowCase(ExecState* exec) const
>         return vm.smallStrings.nullString();
>     if (isUndefined())
>         return vm.smallStrings.undefinedString();
>+    if (isSymbol()) {
>+        throwTypeError(exec);
>+        return jsEmptyString(exec);
>+    }
> 
>     ASSERT(isCell());
>     JSValue value = asCell()->toPrimitive(exec, PreferString);
>diff --git a/Source/JavaScriptCore/runtime/JSCJSValue.h b/Source/JavaScriptCore/runtime/JSCJSValue.h
>index c1fa0d12bebf113c6ebb444d78e5cc2af0181891..fa6bba56c3e8460682e7adf032a648de8e395633 100644
>--- a/Source/JavaScriptCore/runtime/JSCJSValue.h
>+++ b/Source/JavaScriptCore/runtime/JSCJSValue.h
>@@ -217,6 +217,7 @@ class JSValue {
>     bool isMachineInt() const;
>     bool isNumber() const;
>     bool isString() const;
>+    bool isSymbol() const;
>     bool isPrimitive() const;
>     bool isGetterSetter() const;
>     bool isCustomGetterSetter() const;
>@@ -242,6 +243,7 @@ class JSValue {
>     // been set in the ExecState already.
>     double toNumber(ExecState*) const;
>     JSString* toString(ExecState*) const;
>+    PropertyName toPropertyKey(ExecState*) const;
>     WTF::String toWTFString(ExecState*) const;
>     WTF::String toWTFStringInline(ExecState*) const;
>     JSObject* toObject(ExecState*) const;
>diff --git a/Source/JavaScriptCore/runtime/JSCJSValueInlines.h b/Source/JavaScriptCore/runtime/JSCJSValueInlines.h
>index 1510b4185274e8a27e1d3bdf4ef8d8c713fa0ae8..59625be854c4182e00b135c0b3c427fbee79d4de 100644
>--- a/Source/JavaScriptCore/runtime/JSCJSValueInlines.h
>+++ b/Source/JavaScriptCore/runtime/JSCJSValueInlines.h
>@@ -26,6 +26,7 @@
> #ifndef JSValueInlines_h
> #define JSValueInlines_h
> 
>+#include "Identifier.h"
> #include "InternalFunction.h"
> #include "JSCJSValue.h"
> #include "JSCellInlines.h"
>@@ -549,9 +550,14 @@ inline bool JSValue::isString() const
>     return isCell() && asCell()->isString();
> }
> 
>+inline bool JSValue::isSymbol() const
>+{
>+    return isCell() && asCell()->isSymbol();
>+}
>+
> inline bool JSValue::isPrimitive() const
> {
>-    return !isCell() || asCell()->isString();
>+    return !isCell() || asCell()->isString() || asCell()->isSymbol();
> }
> 
> inline bool JSValue::isGetterSetter() const
>@@ -604,6 +610,17 @@ ALWAYS_INLINE bool JSValue::getUInt32(uint32_t& v) const
>     return false;
> }
> 
>+inline PropertyName JSValue::toPropertyKey(ExecState* exec) const
>+{
>+    if (isString())
>+        return asString(*this)->toIdentifier(exec);
>+
>+    JSValue primitive = toPrimitive(exec, PreferString);
>+    if (primitive.isSymbol())
>+        return asSymbol(primitive)->privateName();
>+    return primitive.toString(exec)->toIdentifier(exec);
>+}
>+
> inline JSValue JSValue::toPrimitive(ExecState* exec, PreferredPrimitiveType preferredType) const
> {
>     return isCell() ? asCell()->toPrimitive(exec, preferredType) : asValue();
>@@ -692,7 +709,7 @@ ALWAYS_INLINE bool JSValue::getPropertySlot(ExecState* exec, PropertyName proper
>     // and if it's a string there are special properties to check first.
>     JSObject* object;
>     if (UNLIKELY(!isObject())) {
>-        if (isCell() && asString(*this)->getStringPropertySlot(exec, propertyName, slot))
>+        if (isString() && asString(*this)->getStringPropertySlot(exec, propertyName, slot))
>             return true;
>         object = synthesizePrototype(exec);
>     } else
>@@ -713,7 +730,7 @@ ALWAYS_INLINE JSValue JSValue::get(ExecState* exec, unsigned propertyName, Prope
>     // and if it's a string there are special properties to check first.
>     JSObject* object;
>     if (UNLIKELY(!isObject())) {
>-        if (isCell() && asString(*this)->getStringPropertySlot(exec, propertyName, slot))
>+        if (isString() && asString(*this)->getStringPropertySlot(exec, propertyName, slot))
>             return slot.getValue(exec, propertyName);
>         object = synthesizePrototype(exec);
>     } else
>@@ -806,6 +823,14 @@ ALWAYS_INLINE bool JSValue::equalSlowCaseInline(ExecState* exec, JSValue v1, JSV
>             continue;
>         }
> 
>+        bool sym1 = v1.isSymbol();
>+        bool sym2 = v2.isSymbol();
>+        if (sym1 || sym2) {
>+            if (sym1 && sym2)
>+                return asSymbol(v1)->privateName().uid() == asSymbol(v2)->privateName().uid();
>+            return false;
>+        }
>+
>         if (s1 || s2) {
>             double d1 = v1.toNumber(exec);
>             double d2 = v2.toNumber(exec);
>@@ -831,6 +856,8 @@ ALWAYS_INLINE bool JSValue::strictEqualSlowCaseInline(ExecState* exec, JSValue v
> 
>     if (v1.asCell()->isString() && v2.asCell()->isString())
>         return WTF::equal(*asString(v1)->value(exec).impl(), *asString(v2)->value(exec).impl());
>+    if (v1.asCell()->isSymbol() && v2.asCell()->isSymbol())
>+        return asSymbol(v1)->privateName().uid() == asSymbol(v2)->privateName().uid();
> 
>     return v1 == v2;
> }
>diff --git a/Source/JavaScriptCore/runtime/JSCell.cpp b/Source/JavaScriptCore/runtime/JSCell.cpp
>index 694081db5f17784a54a48e085bad6e13d89f09c8..2c403c813fb38568b0e60ce78989ddea4c953c12 100644
>--- a/Source/JavaScriptCore/runtime/JSCell.cpp
>+++ b/Source/JavaScriptCore/runtime/JSCell.cpp
>@@ -96,7 +96,7 @@ ConstructType JSCell::getConstructData(JSCell*, ConstructData& constructData)
> 
> void JSCell::put(JSCell* cell, ExecState* exec, PropertyName identifier, JSValue value, PutPropertySlot& slot)
> {
>-    if (cell->isString()) {
>+    if (cell->isString() || cell->isSymbol()) {
>         JSValue(cell).putToPrimitive(exec, identifier, value, slot);
>         return;
>     }
>@@ -106,7 +106,7 @@ void JSCell::put(JSCell* cell, ExecState* exec, PropertyName identifier, JSValue
> 
> void JSCell::putByIndex(JSCell* cell, ExecState* exec, unsigned identifier, JSValue value, bool shouldThrow)
> {
>-    if (cell->isString()) {
>+    if (cell->isString() || cell->isSymbol()) {
>         PutPropertySlot slot(cell, shouldThrow);
>         JSValue(cell).putToPrimitive(exec, Identifier::from(exec, identifier), value, slot);
>         return;
>@@ -138,6 +138,8 @@ JSValue JSCell::toPrimitive(ExecState* exec, PreferredPrimitiveType preferredTyp
> {
>     if (isString())
>         return static_cast<const JSString*>(this)->toPrimitive(exec, preferredType);
>+    if (isSymbol())
>+        return static_cast<const Symbol*>(this)->toPrimitive(exec, preferredType);
>     return static_cast<const JSObject*>(this)->toPrimitive(exec, preferredType);
> }
> 
>@@ -145,6 +147,8 @@ bool JSCell::getPrimitiveNumber(ExecState* exec, double& number, JSValue& value)
> {
>     if (isString())
>         return static_cast<const JSString*>(this)->getPrimitiveNumber(exec, number, value);
>+    if (isSymbol())
>+        return static_cast<const Symbol*>(this)->getPrimitiveNumber(exec, number, value);
>     return static_cast<const JSObject*>(this)->getPrimitiveNumber(exec, number, value);
> }
> 
>@@ -152,6 +156,8 @@ double JSCell::toNumber(ExecState* exec) const
> { 
>     if (isString())
>         return static_cast<const JSString*>(this)->toNumber(exec);
>+    if (isSymbol())
>+        return static_cast<const Symbol*>(this)->toNumber(exec);
>     return static_cast<const JSObject*>(this)->toNumber(exec);
> }
> 
>@@ -159,6 +165,8 @@ JSObject* JSCell::toObject(ExecState* exec, JSGlobalObject* globalObject) const
> {
>     if (isString())
>         return static_cast<const JSString*>(this)->toObject(exec, globalObject);
>+    if (isSymbol())
>+        return static_cast<const Symbol*>(this)->toObject(exec, globalObject);
>     ASSERT(isObject());
>     return jsCast<JSObject*>(const_cast<JSCell*>(this));
> }
>diff --git a/Source/JavaScriptCore/runtime/JSCell.h b/Source/JavaScriptCore/runtime/JSCell.h
>index f57a5c87995ca4c332e28a3657205a2d5c5e101e..4839f64fa1a820eeacb709f98c30b7af7c4e8194 100644
>--- a/Source/JavaScriptCore/runtime/JSCell.h
>+++ b/Source/JavaScriptCore/runtime/JSCell.h
>@@ -85,6 +85,7 @@ class JSCell {
> public:
>     // Querying the type.
>     bool isString() const;
>+    bool isSymbol() const;
>     bool isObject() const;
>     bool isGetterSetter() const;
>     bool isCustomGetterSetter() const;
>diff --git a/Source/JavaScriptCore/runtime/JSCellInlines.h b/Source/JavaScriptCore/runtime/JSCellInlines.h
>index 151ae77adbd9003d974c0376fb6e2080d54cb75e..b2fa4066bd2b50838f79b1ef6cad55b24ac6b7ed 100644
>--- a/Source/JavaScriptCore/runtime/JSCellInlines.h
>+++ b/Source/JavaScriptCore/runtime/JSCellInlines.h
>@@ -35,6 +35,7 @@
> #include "JSString.h"
> #include "MarkedBlock.h"
> #include "Structure.h"
>+#include "Symbol.h"
> #include <wtf/CompilationThread.h>
> 
> namespace JSC {
>@@ -164,6 +165,11 @@ inline bool JSCell::isString() const
>     return m_type == StringType;
> }
> 
>+inline bool JSCell::isSymbol() const
>+{
>+    return m_type == SymbolType;
>+}
>+
> inline bool JSCell::isGetterSetter() const
> {
>     return m_type == GetterSetterType;
>@@ -247,15 +253,19 @@ inline const ClassInfo* JSCell::classInfo() const
> 
> inline bool JSCell::toBoolean(ExecState* exec) const
> {
>-    if (isString()) 
>+    if (isString())
>         return static_cast<const JSString*>(this)->toBoolean();
>+    if (isSymbol())
>+        return static_cast<const Symbol*>(this)->toBoolean();
>     return !structure()->masqueradesAsUndefined(exec->lexicalGlobalObject());
> }
> 
> inline TriState JSCell::pureToBoolean() const
> {
>-    if (isString()) 
>+    if (isString())
>         return static_cast<const JSString*>(this)->toBoolean() ? TrueTriState : FalseTriState;
>+    if (isSymbol())
>+        return static_cast<const Symbol*>(this)->toBoolean() ? TrueTriState : FalseTriState;
>     return MixedTriState;
> }
> 
>diff --git a/Source/JavaScriptCore/runtime/JSGlobalObject.cpp b/Source/JavaScriptCore/runtime/JSGlobalObject.cpp
>index 8312c0094056283987640075ea3062771c21c0fc..82f5f9da4fd39af5d87987fa9b283c35cf78399c 100644
>--- a/Source/JavaScriptCore/runtime/JSGlobalObject.cpp
>+++ b/Source/JavaScriptCore/runtime/JSGlobalObject.cpp
>@@ -94,9 +94,6 @@
> #include "MapPrototype.h"
> #include "MathObject.h"
> #include "Microtask.h"
>-#include "NameConstructor.h"
>-#include "NameInstance.h"
>-#include "NamePrototype.h"
> #include "NativeErrorConstructor.h"
> #include "NativeErrorPrototype.h"
> #include "NullGetterFunction.h"
>@@ -118,6 +115,9 @@
> #include "StrictEvalActivation.h"
> #include "StringConstructor.h"
> #include "StringPrototype.h"
>+#include "Symbol.h"
>+#include "SymbolConstructor.h"
>+#include "SymbolPrototype.h"
> #include "VariableWatchpointSetInlines.h"
> #include "WeakMapConstructor.h"
> #include "WeakMapPrototype.h"
>@@ -425,15 +425,6 @@ void JSGlobalObject::init(VM& vm)
>     JSConsole* consoleObject = JSConsole::create(vm, m_consoleStructure.get());
>     putDirectWithoutTransition(vm, Identifier(exec, "console"), consoleObject, DontEnum);
>     
>-    if (m_experimentsEnabled) {
>-        NamePrototype* privateNamePrototype = NamePrototype::create(exec, NamePrototype::createStructure(vm, this, m_objectPrototype.get()));
>-        m_privateNameStructure.set(vm, this, NameInstance::createStructure(vm, this, privateNamePrototype));
>-        
>-        JSCell* privateNameConstructor = NameConstructor::create(vm, NameConstructor::createStructure(vm, this, m_functionPrototype.get()), privateNamePrototype);
>-        privateNamePrototype->putDirectWithoutTransition(vm, vm.propertyNames->constructor, privateNameConstructor, DontEnum);
>-        putDirectWithoutTransition(vm, Identifier(exec, "Name"), privateNameConstructor, DontEnum);
>-    }
>-    
>     resetPrototype(vm, prototype());
> }
> 
>@@ -695,7 +686,7 @@ void JSGlobalObject::visitChildren(JSCell* cell, SlotVisitor& visitor)
>     visitor.append(&thisObject->m_functionStructure);
>     visitor.append(&thisObject->m_boundFunctionStructure);
>     visitor.append(&thisObject->m_namedFunctionStructure);
>-    visitor.append(&thisObject->m_privateNameStructure);
>+    visitor.append(&thisObject->m_symbolObjectStructure);
>     visitor.append(&thisObject->m_regExpMatchesArrayStructure);
>     visitor.append(&thisObject->m_regExpStructure);
>     visitor.append(&thisObject->m_consoleStructure);
>diff --git a/Source/JavaScriptCore/runtime/JSGlobalObject.h b/Source/JavaScriptCore/runtime/JSGlobalObject.h
>index d1d4497fabba71d5ed2e24c6a34ad43e1511f6c5..9f504f7d11cccef0c62cac6992a70b4a4797182a 100644
>--- a/Source/JavaScriptCore/runtime/JSGlobalObject.h
>+++ b/Source/JavaScriptCore/runtime/JSGlobalObject.h
>@@ -35,6 +35,7 @@
> #include "StringPrototype.h"
> #include "StructureChain.h"
> #include "StructureRareDataInlines.h"
>+#include "SymbolPrototype.h"
> #include "VM.h"
> #include "Watchpoint.h"
> #include <JavaScriptCore/JSBase.h>
>@@ -91,6 +92,7 @@
>     macro(Map, map, map, JSMap, Map) \
>     macro(Date, date, date, DateInstance, Date) \
>     macro(String, string, stringObject, StringObject, String) \
>+    macro(Symbol, symbol, symbolObject, SymbolObject, Symbol) \
>     macro(Boolean, boolean, booleanObject, BooleanObject, Boolean) \
>     macro(Number, number, numberObject, NumberObject, Number) \
>     macro(Error, error, error, ErrorInstance, Error) \
>@@ -393,6 +395,7 @@ class JSGlobalObject : public JSSegmentedVariableObject {
>     ArrayPrototype* arrayPrototype() const { return m_arrayPrototype.get(); }
>     BooleanPrototype* booleanPrototype() const { return m_booleanPrototype.get(); }
>     StringPrototype* stringPrototype() const { return m_stringPrototype.get(); }
>+    SymbolPrototype* symbolPrototype() const { return m_symbolPrototype.get(); }
>     NumberPrototype* numberPrototype() const { return m_numberPrototype.get(); }
>     DatePrototype* datePrototype() const { return m_datePrototype.get(); }
>     RegExpPrototype* regExpPrototype() const { return m_regExpPrototype.get(); }
>@@ -451,6 +454,7 @@ class JSGlobalObject : public JSSegmentedVariableObject {
>     Structure* regExpStructure() const { return m_regExpStructure.get(); }
>     Structure* setStructure() const { return m_setStructure.get(); }
>     Structure* stringObjectStructure() const { return m_stringObjectStructure.get(); }
>+    Structure* symbolObjectStructure() const { return m_symbolObjectStructure.get(); }
>     Structure* iteratorResultStructure() const { return m_iteratorResultStructure.get(); }
>     static ptrdiff_t iteratorResultStructureOffset() { return OBJECT_OFFSETOF(JSGlobalObject, m_iteratorResultStructure); }
> 
>diff --git a/Source/JavaScriptCore/runtime/JSONObject.cpp b/Source/JavaScriptCore/runtime/JSONObject.cpp
>index 4974e882dc88ff2482d5a33d38ea02ac3140ad3b..6bcf6e54321961f4e33a6b4c421ec39587195bda 100644
>--- a/Source/JavaScriptCore/runtime/JSONObject.cpp
>+++ b/Source/JavaScriptCore/runtime/JSONObject.cpp
>@@ -228,7 +228,9 @@ JSValue PropertyNameForFunctionCall::value(ExecState* exec) const
>                     continue;
>             }
> 
>-            m_arrayReplacerPropertyNames.add(name.toString(exec)->toIdentifier(exec));
>+            // Don't insert Symbol into m_arrayReplacerPropertyNames.
>+            if (name.isNumber() || name.isString())
>+                m_arrayReplacerPropertyNames.add(name.toString(exec)->toIdentifier(exec));
>         }
>         return;
>     }
>diff --git a/Source/JavaScriptCore/runtime/JSSymbolTableObject.cpp b/Source/JavaScriptCore/runtime/JSSymbolTableObject.cpp
>index 38d8b7fb30fa5185d006b645c5fe6d138f052c44..b8fb2282afae87ecc4110245ce9bb873e950f0ff 100644
>--- a/Source/JavaScriptCore/runtime/JSSymbolTableObject.cpp
>+++ b/Source/JavaScriptCore/runtime/JSSymbolTableObject.cpp
>@@ -61,7 +61,7 @@ void JSSymbolTableObject::getOwnNonIndexPropertyNames(JSObject* object, ExecStat
>         ConcurrentJITLocker locker(thisObject->symbolTable()->m_lock);
>         SymbolTable::Map::iterator end = thisObject->symbolTable()->end(locker);
>         for (SymbolTable::Map::iterator it = thisObject->symbolTable()->begin(locker); it != end; ++it) {
>-            if (it->key->isEmptyUnique())
>+            if (it->key->isUnique())
>                 continue;
>             if (!(it->value.getAttributes() & DontEnum) || shouldIncludeDontEnumProperties(mode))
>                 propertyNames.add(Identifier(exec, it->key.get()));
>diff --git a/Source/JavaScriptCore/runtime/JSType.h b/Source/JavaScriptCore/runtime/JSType.h
>index ab14172b0c019fa2c58d67add68e9050a52eae2d..f86b54cf762d29bc3b78f5a247e912ed0688a325 100644
>--- a/Source/JavaScriptCore/runtime/JSType.h
>+++ b/Source/JavaScriptCore/runtime/JSType.h
>@@ -33,6 +33,7 @@ enum JSType : uint8_t {
>     // The CellType value must come before any JSType that is a JSCell.
>     CellType,
>     StringType,
>+    SymbolType,
> 
>     GetterSetterType,
>     CustomGetterSetterType,
>@@ -52,7 +53,6 @@ enum JSType : uint8_t {
>     FinalObjectType,
>     JSCalleeType,
>     JSFunctionType,
>-    NameInstanceType,
>     NumberObjectType,
>     ErrorInstanceType,
>     PureForwardingProxyType,
>diff --git a/Source/JavaScriptCore/runtime/JSTypeInfo.h b/Source/JavaScriptCore/runtime/JSTypeInfo.h
>index 49118f34cb8111fc1798796bd4815884a6c7d024..f69596890922e5f426e11e57da2515962a6392d7 100644
>--- a/Source/JavaScriptCore/runtime/JSTypeInfo.h
>+++ b/Source/JavaScriptCore/runtime/JSTypeInfo.h
>@@ -77,7 +77,6 @@ class TypeInfo {
>     static bool isObject(JSType type) { return type >= ObjectType; }
>     bool isFinalObject() const { return type() == FinalObjectType; }
>     bool isNumberObject() const { return type() == NumberObjectType; }
>-    bool isName() const { return type() == NameInstanceType; }
> 
>     unsigned flags() const { return (static_cast<unsigned>(m_flags2) << 8) | static_cast<unsigned>(m_flags); }
>     bool masqueradesAsUndefined() const { return isSetOnFlags1(MasqueradesAsUndefined); }
>diff --git a/Source/JavaScriptCore/runtime/NameConstructor.cpp b/Source/JavaScriptCore/runtime/NameConstructor.cpp
>deleted file mode 100644
>index e497a96ecc37ada4918c4c03e822b59e4cf23255..0000000000000000000000000000000000000000
>--- a/Source/JavaScriptCore/runtime/NameConstructor.cpp
>+++ /dev/null
>@@ -1,69 +0,0 @@
>-/*
>- * Copyright (C) 2012 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#include "config.h"
>-#include "NameConstructor.h"
>-
>-#include "JSGlobalObject.h"
>-#include "NamePrototype.h"
>-#include "JSCInlines.h"
>-
>-namespace JSC {
>-
>-STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(NameConstructor);
>-
>-const ClassInfo NameConstructor::s_info = { "Function", &Base::s_info, 0, CREATE_METHOD_TABLE(NameConstructor) };
>-
>-NameConstructor::NameConstructor(VM& vm, Structure* structure)
>-    : InternalFunction(vm, structure)
>-{
>-}
>-
>-void NameConstructor::finishCreation(VM& vm, NamePrototype* prototype)
>-{
>-    Base::finishCreation(vm, prototype->classInfo()->className);
>-    putDirectWithoutTransition(vm, vm.propertyNames->prototype, prototype, DontEnum | DontDelete | ReadOnly);
>-    putDirectWithoutTransition(vm, vm.propertyNames->length, jsNumber(1), DontDelete | ReadOnly | DontEnum);
>-}
>-
>-static EncodedJSValue JSC_HOST_CALL constructPrivateName(ExecState* exec)
>-{
>-    JSValue publicName = exec->argument(0);
>-    return JSValue::encode(NameInstance::create(exec->vm(), exec->lexicalGlobalObject()->privateNameStructure(), publicName.toString(exec)));
>-}
>-
>-ConstructType NameConstructor::getConstructData(JSCell*, ConstructData& constructData)
>-{
>-    constructData.native.function = constructPrivateName;
>-    return ConstructTypeHost;
>-}
>-
>-CallType NameConstructor::getCallData(JSCell*, CallData& callData)
>-{
>-    callData.native.function = constructPrivateName;
>-    return CallTypeHost;
>-}
>-
>-} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/NameConstructor.h b/Source/JavaScriptCore/runtime/NameConstructor.h
>deleted file mode 100644
>index 8e20f28fc88e5a06029463095a54c039551d4592..0000000000000000000000000000000000000000
>--- a/Source/JavaScriptCore/runtime/NameConstructor.h
>+++ /dev/null
>@@ -1,65 +0,0 @@
>-/*
>- * Copyright (C) 2012 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#ifndef NameConstructor_h
>-#define NameConstructor_h
>-
>-#include "InternalFunction.h"
>-#include "NameInstance.h"
>-
>-namespace JSC {
>-
>-class NamePrototype;
>-
>-class NameConstructor : public InternalFunction {
>-public:
>-    typedef InternalFunction Base;
>-
>-    static NameConstructor* create(VM& vm, Structure* structure, NamePrototype* prototype)
>-    {
>-        NameConstructor* constructor = new (NotNull, allocateCell<NameConstructor>(vm.heap)) NameConstructor(vm, structure);
>-        constructor->finishCreation(vm, prototype);
>-        return constructor;
>-    }
>-
>-    DECLARE_INFO;
>-
>-    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype) 
>-    { 
>-        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), info()); 
>-    }
>-
>-protected:
>-    void finishCreation(VM&, NamePrototype*);
>-    
>-private:
>-    NameConstructor(VM&, Structure*);
>-    static ConstructType getConstructData(JSCell*, ConstructData&);
>-    static CallType getCallData(JSCell*, CallData&);
>-};
>-
>-} // namespace JSC
>-
>-#endif // NameConstructor_h
>diff --git a/Source/JavaScriptCore/runtime/NameInstance.cpp b/Source/JavaScriptCore/runtime/NameInstance.cpp
>deleted file mode 100644
>index f6d7f7808542194663ecc87eff5dfe770581b0f6..0000000000000000000000000000000000000000
>--- a/Source/JavaScriptCore/runtime/NameInstance.cpp
>+++ /dev/null
>@@ -1,47 +0,0 @@
>-/*
>- * Copyright (C) 2012 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#include "config.h"
>-#include "NameInstance.h"
>-
>-#include "JSScope.h"
>-#include "JSCInlines.h"
>-
>-namespace JSC {
>-
>-const ClassInfo NameInstance::s_info = { "Name", &Base::s_info, 0, CREATE_METHOD_TABLE(NameInstance) };
>-
>-NameInstance::NameInstance(VM& vm, Structure* structure, JSString* nameString)
>-    : Base(vm, structure)
>-{
>-    m_nameString.set(vm, this, nameString);
>-}
>-
>-void NameInstance::destroy(JSCell* cell)
>-{
>-    static_cast<NameInstance*>(cell)->NameInstance::~NameInstance();
>-}
>-
>-} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/NameInstance.h b/Source/JavaScriptCore/runtime/NameInstance.h
>deleted file mode 100644
>index 55842d52b89d3de7082713ab1d8dee7b318c057c..0000000000000000000000000000000000000000
>--- a/Source/JavaScriptCore/runtime/NameInstance.h
>+++ /dev/null
>@@ -1,77 +0,0 @@
>-/*
>- * Copyright (C) 2012 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#ifndef NameInstance_h
>-#define NameInstance_h
>-
>-#include "JSDestructibleObject.h"
>-#include "PrivateName.h"
>-
>-namespace JSC {
>-
>-class NameInstance : public JSDestructibleObject {
>-public:
>-    typedef JSDestructibleObject Base;
>-
>-    DECLARE_INFO;
>-
>-    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>-    {
>-        return Structure::create(vm, globalObject, prototype, TypeInfo(NameInstanceType, StructureFlags), info());
>-    }
>-
>-    static NameInstance* create(VM& vm, Structure* structure, JSString* nameString)
>-    {
>-        NameInstance* name = new (NotNull, allocateCell<NameInstance>(vm.heap)) NameInstance(vm, structure, nameString);
>-        name->finishCreation(vm);
>-        return name;
>-    }
>-
>-    const PrivateName& privateName() { return m_privateName; }
>-    JSString* nameString() { return m_nameString.get(); }
>-
>-protected:
>-    static void destroy(JSCell*);
>-
>-    NameInstance(VM&, Structure*, JSString*);
>-
>-    void finishCreation(VM& vm)
>-    {
>-        Base::finishCreation(vm);
>-        ASSERT(inherits(info()));
>-    }
>-
>-    PrivateName m_privateName;
>-    WriteBarrier<JSString> m_nameString;
>-};
>-
>-inline bool isName(JSValue v)
>-{
>-    return v.isCell() && v.asCell()->type() == NameInstanceType;
>-}
>-
>-} // namespace JSC
>-
>-#endif // NameInstance_h
>diff --git a/Source/JavaScriptCore/runtime/NamePrototype.cpp b/Source/JavaScriptCore/runtime/NamePrototype.cpp
>deleted file mode 100644
>index bf08d9aaea396932994f47e5f80d7b94f1521d1c..0000000000000000000000000000000000000000
>--- a/Source/JavaScriptCore/runtime/NamePrototype.cpp
>+++ /dev/null
>@@ -1,81 +0,0 @@
>-/*
>- * Copyright (C) 2012 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#include "config.h"
>-#include "NamePrototype.h"
>-
>-#include "Error.h"
>-#include "JSCInlines.h"
>-
>-namespace JSC {
>-
>-static EncodedJSValue JSC_HOST_CALL privateNameProtoFuncToString(ExecState*);
>-
>-}
>-
>-#include "NamePrototype.lut.h"
>-
>-namespace JSC {
>-
>-const ClassInfo NamePrototype::s_info = { "Name", &Base::s_info, &privateNamePrototypeTable, CREATE_METHOD_TABLE(NamePrototype) };
>-
>-/* Source for NamePrototype.lut.h
>-@begin privateNamePrototypeTable
>-  toString          privateNameProtoFuncToString         DontEnum|Function 0
>-@end
>-*/
>-
>-NamePrototype::NamePrototype(ExecState* exec, Structure* structure)
>-    : Base(exec->vm(), structure, jsEmptyString(exec))
>-{
>-}
>-
>-void NamePrototype::finishCreation(VM& vm)
>-{
>-    Base::finishCreation(vm);
>-    ASSERT(inherits(info()));
>-}
>-
>-bool NamePrototype::getOwnPropertySlot(JSObject* object, ExecState* exec, PropertyName propertyName, PropertySlot &slot)
>-{
>-    return getStaticFunctionSlot<Base>(exec, privateNamePrototypeTable, jsCast<NamePrototype*>(object), propertyName, slot);
>-}
>-
>-// ------------------------------ Functions ---------------------------
>-
>-EncodedJSValue JSC_HOST_CALL privateNameProtoFuncToString(ExecState* exec)
>-{
>-    JSValue thisValue = exec->thisValue();
>-    if (!thisValue.isObject())
>-        return throwVMTypeError(exec);
>-
>-    JSObject* thisObject = asObject(thisValue);
>-    if (!thisObject->inherits(NameInstance::info()))
>-        return throwVMTypeError(exec);
>-
>-    return JSValue::encode(jsCast<NameInstance*>(thisObject)->nameString());
>-}
>-
>-} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/NamePrototype.h b/Source/JavaScriptCore/runtime/NamePrototype.h
>deleted file mode 100644
>index d4b947f72d3b03cfeaf0177f15d7e55b38aa6946..0000000000000000000000000000000000000000
>--- a/Source/JavaScriptCore/runtime/NamePrototype.h
>+++ /dev/null
>@@ -1,64 +0,0 @@
>-/*
>- * Copyright (C) 2012 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#ifndef NamePrototype_h
>-#define NamePrototype_h
>-
>-#include "NameInstance.h"
>-
>-namespace JSC {
>-
>-class NamePrototype : public NameInstance {
>-public:
>-    typedef NameInstance Base;
>-
>-    static NamePrototype* create(ExecState* exec, Structure* structure)
>-    {
>-        VM& vm = exec->vm();
>-        NamePrototype* prototype = new (NotNull, allocateCell<NamePrototype>(vm.heap)) NamePrototype(exec, structure);
>-        prototype->finishCreation(vm);
>-        return prototype;
>-    }
>-    
>-    DECLARE_INFO;
>-
>-    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>-    {
>-        return Structure::create(vm, globalObject, prototype, TypeInfo(NameInstanceType, StructureFlags), info());
>-    }
>-
>-protected:
>-    NamePrototype(ExecState*, Structure*);
>-    void finishCreation(VM&);
>-
>-    static const unsigned StructureFlags = OverridesGetOwnPropertySlot | NameInstance::StructureFlags;
>-
>-private:
>-    static bool getOwnPropertySlot(JSObject*, ExecState*, PropertyName, PropertySlot&);
>-};
>-
>-} // namespace JSC
>-
>-#endif // NamePrototype_h
>diff --git a/Source/JavaScriptCore/runtime/ObjectConstructor.cpp b/Source/JavaScriptCore/runtime/ObjectConstructor.cpp
>index a87a4fc3cc906de05c0103083b25d3ddc2c8b2ba..602e575289e16cdc16a0bba349785f2e27ef17dd 100644
>--- a/Source/JavaScriptCore/runtime/ObjectConstructor.cpp
>+++ b/Source/JavaScriptCore/runtime/ObjectConstructor.cpp
>@@ -173,7 +173,7 @@ EncodedJSValue JSC_HOST_CALL objectConstructorGetOwnPropertyDescriptor(ExecState
> {
>     if (!exec->argument(0).isObject())
>         return throwVMError(exec, createTypeError(exec, ASCIILiteral("Requested property descriptor of a value that is not an object.")));
>-    Identifier propertyName = exec->argument(1).toString(exec)->toIdentifier(exec);
>+    PropertyName propertyName = exec->argument(1).toPropertyKey(exec);
>     if (exec->hadException())
>         return JSValue::encode(jsNull());
>     JSObject* object = asObject(exec->argument(0));
>@@ -316,7 +316,7 @@ EncodedJSValue JSC_HOST_CALL objectConstructorDefineProperty(ExecState* exec)
>     if (!exec->argument(0).isObject())
>         return throwVMError(exec, createTypeError(exec, ASCIILiteral("Properties can only be defined on Objects.")));
>     JSObject* O = asObject(exec->argument(0));
>-    Identifier propertyName = exec->argument(1).toString(exec)->toIdentifier(exec);
>+    PropertyName propertyName = exec->argument(1).toPropertyKey(exec);
>     if (exec->hadException())
>         return JSValue::encode(jsNull());
>     PropertyDescriptor descriptor;
>diff --git a/Source/JavaScriptCore/runtime/ObjectPrototype.cpp b/Source/JavaScriptCore/runtime/ObjectPrototype.cpp
>index 33b4420fbccf8b4002d451f3a00db4948f5fb84c..a74b2a55fc4c96a7f23693fcd06107a6fb4a0688 100644
>--- a/Source/JavaScriptCore/runtime/ObjectPrototype.cpp
>+++ b/Source/JavaScriptCore/runtime/ObjectPrototype.cpp
>@@ -85,7 +85,7 @@ EncodedJSValue JSC_HOST_CALL objectProtoFuncValueOf(ExecState* exec)
> EncodedJSValue JSC_HOST_CALL objectProtoFuncHasOwnProperty(ExecState* exec)
> {
>     JSValue thisValue = exec->thisValue().toThis(exec, StrictMode);
>-    return JSValue::encode(jsBoolean(thisValue.toObject(exec)->hasOwnProperty(exec, exec->argument(0).toString(exec)->toIdentifier(exec))));
>+    return JSValue::encode(jsBoolean(thisValue.toObject(exec)->hasOwnProperty(exec, exec->argument(0).toPropertyKey(exec))));
> }
> 
> EncodedJSValue JSC_HOST_CALL objectProtoFuncIsPrototypeOf(ExecState* exec)
>@@ -122,7 +122,7 @@ EncodedJSValue JSC_HOST_CALL objectProtoFuncDefineGetter(ExecState* exec)
>     descriptor.setGetter(get);
>     descriptor.setEnumerable(true);
>     descriptor.setConfigurable(true);
>-    thisObject->methodTable(exec->vm())->defineOwnProperty(thisObject, exec, exec->argument(0).toString(exec)->toIdentifier(exec), descriptor, false);
>+    thisObject->methodTable(exec->vm())->defineOwnProperty(thisObject, exec, exec->argument(0).toPropertyKey(exec), descriptor, false);
> 
>     return JSValue::encode(jsUndefined());
> }
>@@ -142,7 +142,7 @@ EncodedJSValue JSC_HOST_CALL objectProtoFuncDefineSetter(ExecState* exec)
>     descriptor.setSetter(set);
>     descriptor.setEnumerable(true);
>     descriptor.setConfigurable(true);
>-    thisObject->methodTable(exec->vm())->defineOwnProperty(thisObject, exec, exec->argument(0).toString(exec)->toIdentifier(exec), descriptor, false);
>+    thisObject->methodTable(exec->vm())->defineOwnProperty(thisObject, exec, exec->argument(0).toPropertyKey(exec), descriptor, false);
> 
>     return JSValue::encode(jsUndefined());
> }
>@@ -154,7 +154,7 @@ EncodedJSValue JSC_HOST_CALL objectProtoFuncLookupGetter(ExecState* exec)
>         return JSValue::encode(jsUndefined());
> 
>     PropertySlot slot(thisObject);
>-    if (thisObject->getPropertySlot(exec, exec->argument(0).toString(exec)->toIdentifier(exec), slot)
>+    if (thisObject->getPropertySlot(exec, exec->argument(0).toPropertyKey(exec), slot)
>         && slot.isAccessor()) {
>         GetterSetter* getterSetter = slot.getterSetter();
>         return getterSetter->isGetterNull() ? JSValue::encode(jsUndefined()) : JSValue::encode(getterSetter->getter());
>@@ -170,7 +170,7 @@ EncodedJSValue JSC_HOST_CALL objectProtoFuncLookupSetter(ExecState* exec)
>         return JSValue::encode(jsUndefined());
> 
>     PropertySlot slot(thisObject);
>-    if (thisObject->getPropertySlot(exec, exec->argument(0).toString(exec)->toIdentifier(exec), slot)
>+    if (thisObject->getPropertySlot(exec, exec->argument(0).toPropertyKey(exec), slot)
>         && slot.isAccessor()) {
>         GetterSetter* getterSetter = slot.getterSetter();
>         return getterSetter->isSetterNull() ? JSValue::encode(jsUndefined()) : JSValue::encode(getterSetter->setter());
>@@ -182,7 +182,7 @@ EncodedJSValue JSC_HOST_CALL objectProtoFuncLookupSetter(ExecState* exec)
> EncodedJSValue JSC_HOST_CALL objectProtoFuncPropertyIsEnumerable(ExecState* exec)
> {
>     JSObject* thisObject = exec->thisValue().toThis(exec, StrictMode).toObject(exec);
>-    Identifier propertyName = exec->argument(0).toString(exec)->toIdentifier(exec);
>+    PropertyName propertyName = exec->argument(0).toPropertyKey(exec);
> 
>     PropertyDescriptor descriptor;
>     bool enumerable = thisObject->getOwnPropertyDescriptor(exec, propertyName, descriptor) && descriptor.enumerable();
>diff --git a/Source/JavaScriptCore/runtime/Operations.cpp b/Source/JavaScriptCore/runtime/Operations.cpp
>index 36d832f4420b73e316ad81820c4fc34bb177146a..0c9ccb6e39dd12dc0ea60d9dcad38d846c4a18c7 100644
>--- a/Source/JavaScriptCore/runtime/Operations.cpp
>+++ b/Source/JavaScriptCore/runtime/Operations.cpp
>@@ -65,6 +65,8 @@ JSValue jsTypeStringForValue(VM& vm, JSGlobalObject* globalObject, JSValue v)
>         return vm.smallStrings.numberString();
>     if (v.isString())
>         return vm.smallStrings.stringString();
>+    if (v.isSymbol())
>+        return vm.smallStrings.symbolString();
>     if (v.isObject()) {
>         // Return "undefined" for objects that should be treated
>         // as null when doing comparisons.
>@@ -89,7 +91,7 @@ bool jsIsObjectType(CallFrame* callFrame, JSValue v)
>         return v.isNull();
> 
>     JSType type = v.asCell()->type();
>-    if (type == StringType)
>+    if (type == StringType || type == SymbolType)
>         return false;
>     if (type >= ObjectType) {
>         if (asObject(v)->structure(callFrame->vm())->masqueradesAsUndefined(callFrame->lexicalGlobalObject()))
>diff --git a/Source/JavaScriptCore/runtime/PrivateName.h b/Source/JavaScriptCore/runtime/PrivateName.h
>index 55ee634d2a93a5952c71eb0ffd625c7581c0eb16..8272c7a472361b99aba37aa1bf13f72e92361dc4 100644
>--- a/Source/JavaScriptCore/runtime/PrivateName.h
>+++ b/Source/JavaScriptCore/runtime/PrivateName.h
>@@ -33,13 +33,19 @@
> class PrivateName {
> public:
>     PrivateName()
>-        : m_impl(StringImpl::createEmptyUnique())
>+        : m_impl(StringImpl::createUniqueEmpty())
>     {
>+        ASSERT(m_impl->isUnique());
>+    }
>+    PrivateName(const String& description)
>+        : m_impl(StringImpl::createUnique(description.impl()))
>+    {
>+        ASSERT(m_impl->isUnique());
>     }
>     explicit PrivateName(StringImpl* uid)
>         : m_impl(uid)
>     {
>-        ASSERT(m_impl->isEmptyUnique());
>+        ASSERT(m_impl->isUnique());
>     }
> 
>     AtomicStringImpl* uid() const { return static_cast<AtomicStringImpl*>(m_impl.get()); }
>diff --git a/Source/JavaScriptCore/runtime/PropertyMapHashTable.h b/Source/JavaScriptCore/runtime/PropertyMapHashTable.h
>index d7334c0aedc0fea55ecd1743cf4e9281045b7616..0370a3548da986d0411313e04dac2d15c6ba0904 100644
>--- a/Source/JavaScriptCore/runtime/PropertyMapHashTable.h
>+++ b/Source/JavaScriptCore/runtime/PropertyMapHashTable.h
>@@ -271,7 +271,7 @@ inline PropertyTable::const_iterator PropertyTable::end() const
> inline PropertyTable::find_iterator PropertyTable::find(const KeyType& key)
> {
>     ASSERT(key);
>-    ASSERT(key->isAtomic() || key->isEmptyUnique());
>+    ASSERT(key->isAtomic() || key->isUnique());
>     unsigned hash = key->existingHash();
>     unsigned step = 0;
> 
>@@ -305,7 +305,7 @@ inline PropertyTable::find_iterator PropertyTable::find(const KeyType& key)
> inline PropertyTable::ValueType* PropertyTable::get(const KeyType& key)
> {
>     ASSERT(key);
>-    ASSERT(key->isAtomic() || key->isEmptyUnique());
>+    ASSERT(key->isAtomic() || key->isUnique());
> 
>     if (!m_keyCount)
>         return nullptr;
>diff --git a/Source/JavaScriptCore/runtime/PropertyName.h b/Source/JavaScriptCore/runtime/PropertyName.h
>index 22a8ff850fe04b6ed400a1edfdbe2bbfddad2e58..3074c72e1070133b97b03b1dff4a43de132fc0a6 100644
>--- a/Source/JavaScriptCore/runtime/PropertyName.h
>+++ b/Source/JavaScriptCore/runtime/PropertyName.h
>@@ -93,7 +93,7 @@ class PropertyName {
>         : m_impl(static_cast<AtomicStringImpl*>(propertyName.uid()))
>     {
>         ASSERT(m_impl);
>-        ASSERT(m_impl->isEmptyUnique());
>+        ASSERT(m_impl->isUnique());
>         ASSERT(m_impl->isAtomic());
>     }
> 
>@@ -104,7 +104,7 @@ class PropertyName {
> 
>     AtomicStringImpl* publicName() const
>     {
>-        return m_impl->isEmptyUnique() ? nullptr : m_impl;
>+        return m_impl->isUnique() ? nullptr : m_impl;
>     }
> 
>     static const uint32_t NotAnIndex = UINT_MAX;
>diff --git a/Source/JavaScriptCore/runtime/SmallStrings.h b/Source/JavaScriptCore/runtime/SmallStrings.h
>index 31b39f0282c0227b3c7320acfebb17948b6472b8..fd2b76a00befb665ba4f8e8ce512d38250d7640a 100644
>--- a/Source/JavaScriptCore/runtime/SmallStrings.h
>+++ b/Source/JavaScriptCore/runtime/SmallStrings.h
>@@ -38,6 +38,7 @@
>     macro(object) \
>     macro(undefined) \
>     macro(string) \
>+    macro(symbol) \
>     macro(true)
> 
> namespace WTF {
>diff --git a/Source/JavaScriptCore/runtime/Structure.cpp b/Source/JavaScriptCore/runtime/Structure.cpp
>index 86d0b6fbdaece3832cc362fb834098dbcee083a4..3fcb426cda0d5bbac3170a8bcb466175f29c7425 100644
>--- a/Source/JavaScriptCore/runtime/Structure.cpp
>+++ b/Source/JavaScriptCore/runtime/Structure.cpp
>@@ -947,7 +947,7 @@ void Structure::getPropertyNamesFromStructure(VM& vm, PropertyNameArray& propert
>     PropertyTable::iterator end = propertyTable()->end();
>     for (PropertyTable::iterator iter = propertyTable()->begin(); iter != end; ++iter) {
>         ASSERT(hasNonEnumerableProperties() || !(iter->attributes & DontEnum));
>-        if (!iter->key->isEmptyUnique() && (!(iter->attributes & DontEnum) || shouldIncludeDontEnumProperties(mode))) {
>+        if (!iter->key->isUnique() && (!(iter->attributes & DontEnum) || shouldIncludeDontEnumProperties(mode))) {
>             if (knownUnique)
>                 propertyNames.addKnownUnique(iter->key);
>             else
>diff --git a/Source/JavaScriptCore/runtime/StructureInlines.h b/Source/JavaScriptCore/runtime/StructureInlines.h
>index 269292b7d3eac0408ccc79369c64d4e242231fd2..f17bc1b17a401c0dc8918c6db8339c5331085230 100644
>--- a/Source/JavaScriptCore/runtime/StructureInlines.h
>+++ b/Source/JavaScriptCore/runtime/StructureInlines.h
>@@ -168,6 +168,8 @@ inline JSValue Structure::prototypeForLookup(JSGlobalObject* globalObject) const
> {
>     if (isObject())
>         return m_prototype.get();
>+    if (typeInfo().type() == SymbolType)
>+        return globalObject->symbolPrototype();
> 
>     ASSERT(typeInfo().type() == StringType);
>     return globalObject->stringPrototype();
>diff --git a/Source/JavaScriptCore/runtime/Symbol.cpp b/Source/JavaScriptCore/runtime/Symbol.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..f9c623340cdae6becf5187ebe5a909661cf58895
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/Symbol.cpp
>@@ -0,0 +1,96 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "Symbol.h"
>+
>+#include "Error.h"
>+#include "JSCInlines.h"
>+#include "SymbolObject.h"
>+
>+namespace JSC {
>+
>+const ClassInfo Symbol::s_info = { "symbol", nullptr, nullptr, CREATE_METHOD_TABLE(Symbol) };
>+
>+Symbol::Symbol(VM& vm)
>+    : Base(vm, vm.symbolStructure.get())
>+    , m_privateName()
>+{
>+}
>+
>+Symbol::Symbol(VM& vm, const String& string)
>+    : Base(vm, vm.symbolStructure.get())
>+    , m_privateName(string)
>+{
>+}
>+
>+Symbol::Symbol(VM& vm, AtomicStringImpl* uid)
>+    : Base(vm, vm.symbolStructure.get())
>+    , m_privateName(uid)
>+{
>+}
>+
>+inline SymbolObject* SymbolObject::create(VM& vm, JSGlobalObject* globalObject, Symbol* symbol)
>+{
>+    SymbolObject* object = new (NotNull, allocateCell<SymbolObject>(vm.heap)) SymbolObject(vm, globalObject->symbolObjectStructure());
>+    object->finishCreation(vm, symbol);
>+    return object;
>+}
>+
>+JSValue Symbol::toPrimitive(ExecState*, PreferredPrimitiveType) const
>+{
>+    return const_cast<Symbol*>(this);
>+}
>+
>+bool Symbol::toBoolean() const
>+{
>+    return true;
>+}
>+
>+bool Symbol::getPrimitiveNumber(ExecState* exec, double& number, JSValue& result) const
>+{
>+    result = this;
>+    number = toNumber(exec);
>+    return true;
>+}
>+
>+JSObject* Symbol::toObject(ExecState* exec, JSGlobalObject* globalObject) const
>+{
>+    return SymbolObject::create(exec->vm(), globalObject, const_cast<Symbol*>(this));
>+}
>+
>+double Symbol::toNumber(ExecState* exec) const
>+{
>+    throwTypeError(exec);
>+    return 0.0;
>+}
>+
>+void Symbol::destroy(JSCell* cell)
>+{
>+    static_cast<Symbol*>(cell)->Symbol::~Symbol();
>+}
>+
>+} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/Symbol.h b/Source/JavaScriptCore/runtime/Symbol.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..ee20cb3cbc0cd1833203352c71aac4633fbec09e
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/Symbol.h
>@@ -0,0 +1,111 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#ifndef Symbol_h
>+#define Symbol_h
>+
>+#include "JSCell.h"
>+#include "JSString.h"
>+#include "PrivateName.h"
>+
>+namespace JSC {
>+
>+class Symbol : public JSCell {
>+public:
>+    typedef JSCell Base;
>+
>+    DECLARE_INFO;
>+
>+    static const bool needsDestruction = true;
>+    static const bool hasImmortalStructure = true;
>+
>+    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>+    {
>+        return Structure::create(vm, globalObject, prototype, TypeInfo(SymbolType, StructureFlags), info());
>+    }
>+
>+    static Symbol* create(VM& vm)
>+    {
>+        Symbol* symbol = new (NotNull, allocateCell<Symbol>(vm.heap)) Symbol(vm);
>+        symbol->finishCreation(vm);
>+        return symbol;
>+    }
>+
>+    static Symbol* create(ExecState* exec, JSString* description)
>+    {
>+        VM& vm = exec->vm();
>+        String desc = description->value(exec);
>+        Symbol* symbol = new (NotNull, allocateCell<Symbol>(vm.heap)) Symbol(vm, desc);
>+        symbol->finishCreation(vm);
>+        return symbol;
>+    }
>+
>+    static Symbol* create(VM& vm, AtomicStringImpl* uid)
>+    {
>+        Symbol* symbol = new (NotNull, allocateCell<Symbol>(vm.heap)) Symbol(vm, uid);
>+        symbol->finishCreation(vm);
>+        return symbol;
>+    }
>+
>+    const PrivateName& privateName() const { return m_privateName; }
>+    String description() const { return privateName().uid(); }
>+
>+    JSValue toPrimitive(ExecState*, PreferredPrimitiveType) const;
>+    JS_EXPORT_PRIVATE bool toBoolean() const;
>+    bool getPrimitiveNumber(ExecState*, double& number, JSValue&) const;
>+    JSObject* toObject(ExecState*, JSGlobalObject*) const;
>+    double toNumber(ExecState*) const;
>+
>+protected:
>+    static const unsigned StructureFlags = OverridesGetOwnPropertySlot | InterceptsGetOwnPropertySlotByIndexEvenWhenLengthIsNotZero | StructureIsImmortal;
>+
>+    static void destroy(JSCell*);
>+
>+    Symbol(VM&);
>+    Symbol(VM&, const String&);
>+    Symbol(VM&, AtomicStringImpl* uid);
>+
>+    void finishCreation(VM& vm)
>+    {
>+        Base::finishCreation(vm);
>+        ASSERT(inherits(info()));
>+    }
>+
>+    PrivateName m_privateName;
>+};
>+
>+Symbol* asSymbol(JSValue);
>+
>+inline Symbol* asSymbol(JSValue value)
>+{
>+    ASSERT(value.asCell()->isSymbol());
>+    return jsCast<Symbol*>(value.asCell());
>+}
>+
>+} // namespace JSC
>+
>+#endif // Symbol_h
>diff --git a/Source/JavaScriptCore/runtime/SymbolConstructor.cpp b/Source/JavaScriptCore/runtime/SymbolConstructor.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..ba8d3eaa9ee75977ae04ee4e715394b3f0e1666c
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/SymbolConstructor.cpp
>@@ -0,0 +1,83 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "SymbolConstructor.h"
>+
>+#include "Error.h"
>+#include "JSCInlines.h"
>+#include "JSGlobalObject.h"
>+#include "SymbolPrototype.h"
>+
>+namespace JSC {
>+
>+STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(SymbolConstructor);
>+
>+const ClassInfo SymbolConstructor::s_info = { "Function", &Base::s_info, 0, CREATE_METHOD_TABLE(SymbolConstructor) };
>+
>+SymbolConstructor::SymbolConstructor(VM& vm, Structure* structure)
>+    : InternalFunction(vm, structure)
>+{
>+}
>+
>+#define INITIALIZE_WELL_KNOWN_SYMBOLS(name) \
>+    putDirectWithoutTransition(vm, Identifier(&vm, #name), Symbol::create(vm, vm.propertyNames->name##PrivateName.impl()), DontEnum | DontDelete | ReadOnly);
>+
>+void SymbolConstructor::finishCreation(VM& vm, SymbolPrototype* prototype)
>+{
>+    Base::finishCreation(vm, prototype->classInfo()->className);
>+    putDirectWithoutTransition(vm, vm.propertyNames->prototype, prototype, DontEnum | DontDelete | ReadOnly);
>+    putDirectWithoutTransition(vm, vm.propertyNames->length, jsNumber(0), DontDelete | ReadOnly | DontEnum);
>+
>+    JSC_COMMON_PRIVATE_IDENTIFIERS_EACH_WELL_KNOWN_SYMBOL(INITIALIZE_WELL_KNOWN_SYMBOLS)
>+}
>+
>+static EncodedJSValue JSC_HOST_CALL callSymbol(ExecState* exec)
>+{
>+    JSValue description = exec->argument(0);
>+    if (description.isUndefined())
>+        return JSValue::encode(Symbol::create(exec->vm()));
>+    return JSValue::encode(Symbol::create(exec, description.toString(exec)));
>+}
>+
>+static EncodedJSValue JSC_HOST_CALL constructSymbol(ExecState* exec)
>+{
>+    return JSValue::encode(throwTypeError(exec));
>+}
>+
>+ConstructType SymbolConstructor::getConstructData(JSCell*, ConstructData& constructData)
>+{
>+    constructData.native.function = constructSymbol;
>+    return ConstructTypeHost;
>+}
>+
>+CallType SymbolConstructor::getCallData(JSCell*, CallData& callData)
>+{
>+    callData.native.function = callSymbol;
>+    return CallTypeHost;
>+}
>+
>+} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/SymbolConstructor.h b/Source/JavaScriptCore/runtime/SymbolConstructor.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..0ae12d7fdd5c424bb69a26d1dc13ae08084a6839
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/SymbolConstructor.h
>@@ -0,0 +1,66 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#ifndef SymbolConstructor_h
>+#define SymbolConstructor_h
>+
>+#include "InternalFunction.h"
>+#include "Symbol.h"
>+
>+namespace JSC {
>+
>+class SymbolPrototype;
>+
>+class SymbolConstructor : public InternalFunction {
>+public:
>+    typedef InternalFunction Base;
>+
>+    static SymbolConstructor* create(VM& vm, Structure* structure, SymbolPrototype* prototype)
>+    {
>+        SymbolConstructor* constructor = new (NotNull, allocateCell<SymbolConstructor>(vm.heap)) SymbolConstructor(vm, structure);
>+        constructor->finishCreation(vm, prototype);
>+        return constructor;
>+    }
>+
>+    DECLARE_INFO;
>+
>+    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>+    {
>+        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), info());
>+    }
>+
>+protected:
>+    void finishCreation(VM&, SymbolPrototype*);
>+
>+private:
>+    SymbolConstructor(VM&, Structure*);
>+    static ConstructType getConstructData(JSCell*, ConstructData&);
>+    static CallType getCallData(JSCell*, CallData&);
>+};
>+
>+} // namespace JSC
>+
>+#endif // SymbolConstructor_h
>diff --git a/Source/JavaScriptCore/runtime/SymbolObject.cpp b/Source/JavaScriptCore/runtime/SymbolObject.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..a1ef71c3410c847425484ef40ee3465c4ce2d924
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/SymbolObject.cpp
>@@ -0,0 +1,50 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "SymbolObject.h"
>+
>+#include "JSCInlines.h"
>+
>+namespace JSC {
>+
>+STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(SymbolObject);
>+
>+const ClassInfo SymbolObject::s_info = { "Symbol", &JSWrapperObject::s_info, nullptr, CREATE_METHOD_TABLE(SymbolObject) };
>+
>+SymbolObject::SymbolObject(VM& vm, Structure* structure)
>+    : JSWrapperObject(vm, structure)
>+{
>+}
>+
>+void SymbolObject::finishCreation(VM& vm, Symbol* symbol)
>+{
>+    Base::finishCreation(vm);
>+    ASSERT(inherits(info()));
>+    setInternalValue(vm, symbol);
>+}
>+
>+} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/SymbolObject.h b/Source/JavaScriptCore/runtime/SymbolObject.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..4f3c598d9f8c23dbcdeb6b43520f739a92e472d3
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/SymbolObject.h
>@@ -0,0 +1,65 @@
>+/*
>+ *  Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
>+ *  Copyright (C) 2007, 2008 Apple Inc. All rights reserved.
>+ *  Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ *  This library is free software; you can redistribute it and/or
>+ *  modify it under the terms of the GNU Lesser General Public
>+ *  License as published by the Free Software Foundation; either
>+ *  version 2 of the License, or (at your option) any later version.
>+ *
>+ *  This library is distributed in the hope that it will be useful,
>+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
>+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>+ *  Lesser General Public License for more details.
>+ *
>+ *  You should have received a copy of the GNU Lesser General Public
>+ *  License along with this library; if not, write to the Free Software
>+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
>+ *
>+ */
>+
>+#ifndef SymbolObject_h
>+#define SymbolObject_h
>+
>+#include "JSWrapperObject.h"
>+#include "Symbol.h"
>+
>+namespace JSC {
>+
>+class SymbolObject : public JSWrapperObject {
>+public:
>+    typedef JSWrapperObject Base;
>+
>+    static SymbolObject* create(VM& vm, Structure* structure)
>+    {
>+        Symbol* symbol = Symbol::create(vm);
>+        SymbolObject* object = new (NotNull, allocateCell<SymbolObject>(vm.heap)) SymbolObject(vm, structure);
>+        object->finishCreation(vm, symbol);
>+        return object;
>+    }
>+    static SymbolObject* create(VM& vm, Structure* structure, Symbol* symbol)
>+    {
>+        SymbolObject* object = new (NotNull, allocateCell<SymbolObject>(vm.heap)) SymbolObject(vm, structure);
>+        object->finishCreation(vm, symbol);
>+        return object;
>+    }
>+    static SymbolObject* create(VM&, JSGlobalObject*, Symbol*);
>+
>+    DECLARE_EXPORT_INFO;
>+
>+    Symbol* internalValue() const { return asSymbol(JSWrapperObject::internalValue());}
>+
>+    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>+    {
>+        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), info());
>+    }
>+
>+protected:
>+    JS_EXPORT_PRIVATE void finishCreation(VM&, Symbol*);
>+    JS_EXPORT_PRIVATE SymbolObject(VM&, Structure*);
>+};
>+
>+} // namespace JSC
>+
>+#endif // SymbolObject_h
>diff --git a/Source/JavaScriptCore/runtime/SymbolPrototype.cpp b/Source/JavaScriptCore/runtime/SymbolPrototype.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..eec961a30d704f76f703bd5c78cbb5cb0cd01221
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/SymbolPrototype.cpp
>@@ -0,0 +1,110 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "SymbolPrototype.h"
>+
>+#include "Error.h"
>+#include "JSCInlines.h"
>+
>+namespace JSC {
>+
>+static EncodedJSValue JSC_HOST_CALL symbolProtoFuncToString(ExecState*);
>+static EncodedJSValue JSC_HOST_CALL symbolProtoFuncValueOf(ExecState*);
>+
>+}
>+
>+#include "SymbolPrototype.lut.h"
>+
>+namespace JSC {
>+
>+const ClassInfo SymbolPrototype::s_info = { "Symbol", &Base::s_info, &symbolPrototypeTable, CREATE_METHOD_TABLE(SymbolPrototype) };
>+
>+/* Source for SymbolPrototype.lut.h
>+@begin symbolPrototypeTable
>+  toString          symbolProtoFuncToString         DontEnum|Function 0
>+  valueOf           symbolProtoFuncValueOf          DontEnum|Function 0
>+@end
>+*/
>+
>+SymbolPrototype::SymbolPrototype(VM& vm, Structure* structure)
>+    : Base(vm, structure)
>+{
>+}
>+
>+void SymbolPrototype::finishCreation(VM& vm)
>+{
>+    Base::finishCreation(vm);
>+    ASSERT(inherits(info()));
>+}
>+
>+bool SymbolPrototype::getOwnPropertySlot(JSObject* object, ExecState* exec, PropertyName propertyName, PropertySlot &slot)
>+{
>+    return getStaticFunctionSlot<Base>(exec, symbolPrototypeTable, jsCast<SymbolPrototype*>(object), propertyName, slot);
>+}
>+
>+// ------------------------------ Functions ---------------------------
>+
>+EncodedJSValue JSC_HOST_CALL symbolProtoFuncToString(ExecState* exec)
>+{
>+    JSValue thisValue = exec->thisValue();
>+    Symbol* symbol = nullptr;
>+    if (thisValue.isSymbol())
>+        symbol = asSymbol(thisValue);
>+    else if (!thisValue.isObject())
>+        return throwVMTypeError(exec);
>+    else {
>+        JSObject* thisObject = asObject(thisValue);
>+        if (!thisObject->inherits(SymbolObject::info()))
>+            return throwVMTypeError(exec);
>+        symbol = asSymbol(jsCast<SymbolObject*>(thisObject)->internalValue());
>+    }
>+
>+    String description = symbol->description();
>+    StringBuilder builder;
>+    builder.appendLiteral("Symbol(");
>+    builder.append(description);
>+    builder.append(')');
>+    return JSValue::encode(jsString(exec, builder.toString()));
>+}
>+
>+EncodedJSValue JSC_HOST_CALL symbolProtoFuncValueOf(ExecState* exec)
>+{
>+    JSValue thisValue = exec->thisValue();
>+    if (thisValue.isSymbol())
>+        return JSValue::encode(thisValue);
>+
>+    if (!thisValue.isObject())
>+        return throwVMTypeError(exec);
>+
>+    JSObject* thisObject = asObject(thisValue);
>+    if (!thisObject->inherits(SymbolObject::info()))
>+        return throwVMTypeError(exec);
>+
>+    return JSValue::encode(jsCast<SymbolObject*>(thisObject)->internalValue());
>+}
>+
>+} // namespace JSC
>diff --git a/Source/JavaScriptCore/runtime/SymbolPrototype.h b/Source/JavaScriptCore/runtime/SymbolPrototype.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..85a93d3bb07235fda1b9c67ee9b497730fafa32d
>--- /dev/null
>+++ b/Source/JavaScriptCore/runtime/SymbolPrototype.h
>@@ -0,0 +1,66 @@
>+/*
>+ * Copyright (C) 2012 Apple Inc. All rights reserved.
>+ * Copyright (C) 2015 Yusuke Suzuki <utatane.tea@gmail.com>.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#ifndef SymbolPrototype_h
>+#define SymbolPrototype_h
>+
>+#include "Symbol.h"
>+#include "SymbolObject.h"
>+
>+namespace JSC {
>+
>+// In the ES6 spec, Symbol.prototype object is an ordinary JS object, not one of the symbol wrapper object instance.
>+class SymbolPrototype : public JSDestructibleObject {
>+public:
>+    typedef JSDestructibleObject Base;
>+
>+    static SymbolPrototype* create(VM& vm, JSGlobalObject*, Structure* structure)
>+    {
>+        SymbolPrototype* prototype = new (NotNull, allocateCell<SymbolPrototype>(vm.heap)) SymbolPrototype(vm, structure);
>+        prototype->finishCreation(vm);
>+        return prototype;
>+    }
>+
>+    DECLARE_INFO;
>+
>+    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
>+    {
>+        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), info());
>+    }
>+
>+protected:
>+    SymbolPrototype(VM&, Structure*);
>+    void finishCreation(VM&);
>+
>+    static const unsigned StructureFlags = OverridesGetOwnPropertySlot | Base::StructureFlags;
>+
>+private:
>+    static bool getOwnPropertySlot(JSObject*, ExecState*, PropertyName, PropertySlot&);
>+};
>+
>+} // namespace JSC
>+
>+#endif // SymbolPrototype_h
>diff --git a/Source/JavaScriptCore/runtime/VM.cpp b/Source/JavaScriptCore/runtime/VM.cpp
>index 7a883446078185a19e86b6ec9055e9e5734448f2..80ed9ca517455f17f6af5ff837d868687aad795e 100644
>--- a/Source/JavaScriptCore/runtime/VM.cpp
>+++ b/Source/JavaScriptCore/runtime/VM.cpp
>@@ -220,6 +220,7 @@ static bool enableAssembler(ExecutableAllocator& executableAllocator)
>     programExecutableStructure.set(*this, ProgramExecutable::createStructure(*this, 0, jsNull()));
>     functionExecutableStructure.set(*this, FunctionExecutable::createStructure(*this, 0, jsNull()));
>     regExpStructure.set(*this, RegExp::createStructure(*this, 0, jsNull()));
>+    symbolStructure.set(*this, Symbol::createStructure(*this, 0, jsNull()));
>     symbolTableStructure.set(*this, SymbolTable::createStructure(*this, 0, jsNull()));
>     structureChainStructure.set(*this, StructureChain::createStructure(*this, 0, jsNull()));
>     sparseArrayValueMapStructure.set(*this, SparseArrayValueMap::createStructure(*this, 0, jsNull()));
>diff --git a/Source/JavaScriptCore/runtime/VM.h b/Source/JavaScriptCore/runtime/VM.h
>index f8842821761f6ad8abea098d28aa76b0942b6e0f..ce337b8b2417244a6b3b1e45fb845835c3491847 100644
>--- a/Source/JavaScriptCore/runtime/VM.h
>+++ b/Source/JavaScriptCore/runtime/VM.h
>@@ -264,6 +264,7 @@ class VM : public ThreadSafeRefCounted<VM> {
>     Strong<Structure> programExecutableStructure;
>     Strong<Structure> functionExecutableStructure;
>     Strong<Structure> regExpStructure;
>+    Strong<Structure> symbolStructure;
>     Strong<Structure> symbolTableStructure;
>     Strong<Structure> structureChainStructure;
>     Strong<Structure> sparseArrayValueMapStructure;
>diff --git a/Source/WTF/wtf/text/StringImpl.cpp b/Source/WTF/wtf/text/StringImpl.cpp
>index 28a23b42398f98c035c183996357b8260f7bccc2..fd4dcb7b8e07dbdcf9f3257bae7f825c62501e85 100644
>--- a/Source/WTF/wtf/text/StringImpl.cpp
>+++ b/Source/WTF/wtf/text/StringImpl.cpp
>@@ -109,7 +109,7 @@ void StringStats::printStats()
> 
>     STRING_STATS_REMOVE_STRING(*this);
> 
>-    if (isAtomic() && m_length)
>+    if (isAtomic() && length() && !isUnique())
>         AtomicString::remove(this);
> 
>     BufferOwnership ownership = bufferOwnership();
>diff --git a/Source/WTF/wtf/text/StringImpl.h b/Source/WTF/wtf/text/StringImpl.h
>index b66b0cc6c52f0891ffa08d3c6959ddf017e39cd8..368ba1d45ef2e0b68dc61d9e82f1c82c648ba7fd 100644
>--- a/Source/WTF/wtf/text/StringImpl.h
>+++ b/Source/WTF/wtf/text/StringImpl.h
>@@ -280,7 +280,7 @@ class StringImpl {
>         // We expect m_length to be initialized to 0 as we use it
>         // to represent a null terminated buffer.
>         , m_data8(reinterpret_cast<const LChar*>(&m_length))
>-        , m_hashAndFlags(hashAndFlagsForEmptyUnique())
>+        , m_hashAndFlags(hashAndFlagsForUnique(s_hashFlag8BitBuffer | BufferInternal))
>     {
>         ASSERT(m_data8);
> 
>@@ -378,11 +378,20 @@ class StringImpl {
>         return constructInternal<T>(resultImpl, length);
>     }
> 
>-    static Ref<StringImpl> createEmptyUnique()
>+    ALWAYS_INLINE static Ref<StringImpl> createUniqueEmpty()
>     {
>         return adoptRef(*new StringImpl(CreateEmptyUnique));
>     }
> 
>+    ALWAYS_INLINE static Ref<StringImpl> createUnique(PassRefPtr<StringImpl> rep)
>+    {
>+        Ref<StringImpl> string = createSubstringSharingImpl(rep, 0, rep->length());
>+        if (!string->length())
>+            return createUniqueEmpty();
>+        string->m_hashAndFlags = hashAndFlagsForUnique(string->m_hashAndFlags);
>+        return string;
>+    }
>+
>     // Reallocate the StringImpl. The originalString must be only owned by the PassRefPtr,
>     // and the buffer ownership must be BufferInternal. Just like the input pointer of realloc(),
>     // the originalString can't be used after this function.
>@@ -392,6 +401,7 @@ class StringImpl {
>     static unsigned flagsOffset() { return OBJECT_OFFSETOF(StringImpl, m_hashAndFlags); }
>     static unsigned flagIs8Bit() { return s_hashFlag8BitBuffer; }
>     static unsigned flagIsAtomic() { return s_hashFlagIsAtomic; }
>+    static unsigned flagIsUnique() { return s_hashFlagIsUnique; }
>     static unsigned dataOffset() { return OBJECT_OFFSETOF(StringImpl, m_data8); }
> 
>     template<typename CharType, size_t inlineCapacity, typename OverflowHandler>
>@@ -451,16 +461,13 @@ class StringImpl {
> 
>     WTF_EXPORT_STRING_API size_t sizeInBytes() const;
> 
>-    bool isEmptyUnique() const
>-    {
>-        return !length() && !isStatic();
>-    }
>+    bool isUnique() const { return m_hashAndFlags & s_hashFlagIsUnique; }
> 
>     bool isAtomic() const { return m_hashAndFlags & s_hashFlagIsAtomic; }
>     void setIsAtomic(bool isAtomic)
>     {
>         ASSERT(!isStatic());
>-        ASSERT(!isEmptyUnique());
>+        ASSERT(!isUnique());
>         if (isAtomic)
>             m_hashAndFlags |= s_hashFlagIsAtomic;
>         else
>@@ -772,17 +779,18 @@ class StringImpl {
>     template <typename CharType> static Ref<StringImpl> reallocateInternal(PassRefPtr<StringImpl>, unsigned, CharType*&);
>     template <typename CharType> static Ref<StringImpl> createInternal(const CharType*, unsigned);
>     WTF_EXPORT_PRIVATE NEVER_INLINE unsigned hashSlowCase() const;
>-    WTF_EXPORT_PRIVATE unsigned hashAndFlagsForEmptyUnique();
>+    WTF_EXPORT_PRIVATE static unsigned hashAndFlagsForUnique(unsigned flags);
> 
>     // The bottom bit in the ref count indicates a static (immortal) string.
>     static const unsigned s_refCountFlagIsStaticString = 0x1;
>     static const unsigned s_refCountIncrement = 0x2; // This allows us to ref / deref without disturbing the static string flag.
> 
>     // The bottom 6 bits in the hash are flags.
>-    static const unsigned s_flagCount = 6;
>+    static const unsigned s_flagCount = 7;
>     static const unsigned s_flagMask = (1u << s_flagCount) - 1;
>     COMPILE_ASSERT(s_flagCount <= StringHasher::flagCount, StringHasher_reserves_enough_bits_for_StringImpl_flags);
> 
>+    static const unsigned s_hashFlagIsUnique = 1u << 6;
>     static const unsigned s_hashFlag8BitBuffer = 1u << 5;
>     static const unsigned s_hashFlagIsAtomic = 1u << 4;
>     static const unsigned s_hashFlagDidReportCost = 1u << 3;
>diff --git a/Source/WTF/wtf/text/StringStatics.cpp b/Source/WTF/wtf/text/StringStatics.cpp
>index a234ffd2936e67e6a2fc8eeffae09b74195f37f9..65bb6721d743fa1041c292b60f4d0329283d8e51 100644
>--- a/Source/WTF/wtf/text/StringStatics.cpp
>+++ b/Source/WTF/wtf/text/StringStatics.cpp
>@@ -47,17 +47,18 @@ StringImpl* StringImpl::empty()
>     return &emptyString.get();
> }
> 
>-// Set the hash early, so that all empty unique StringImpls have a hash,
>+// Set the hash early, so that all unique StringImpls have a hash,
> // and don't use the normal hashing algorithm - the unique nature of these
> // keys means that we don't need them to match any other string (in fact,
> // that's exactly the oposite of what we want!), and the normal hash would
> // lead to lots of conflicts.
>-unsigned StringImpl::hashAndFlagsForEmptyUnique()
>+unsigned StringImpl::hashAndFlagsForUnique(unsigned flags)
> {
>-    static unsigned s_nextHashAndFlagsForEmptyUnique = BufferInternal | s_hashFlag8BitBuffer | s_hashFlagIsAtomic;
>-    s_nextHashAndFlagsForEmptyUnique += 1 << s_flagCount;
>-    s_nextHashAndFlagsForEmptyUnique |= 1 << 31;
>-    return s_nextHashAndFlagsForEmptyUnique;
>+    static unsigned s_nextHashAndFlagsForUnique = 0;
>+    s_nextHashAndFlagsForUnique += 1 << s_flagCount;
>+    s_nextHashAndFlagsForUnique |= 1 << 31;
>+    unsigned flagsForUnique = (flags & s_flagMask) | s_hashFlagIsAtomic | s_hashFlagIsUnique;
>+    return s_nextHashAndFlagsForUnique | flagsForUnique;
> }
> 
> WTF_EXPORTDATA DEFINE_GLOBAL(AtomicString, nullAtom)

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