https://bugs.webkit.org/show_bug.cgi?id=205723 allowed to declare MediaTime variables as static inside functions without needing a global destructor. It did not eliminate the call to the MediaTime constructor on runtime though. This wasn't a problem for static variables inside functions, as the compiler adds a guard variable to call the constructor the first time the function is called. On the other hand, for variables defined outside of the scope of the function, for them to be initialized the MediaTime constructor would have to be called at runtime from a global constructor, something we're trying to avoid and which generates an error in clang. But again, MediaTime is a simple class with only integral values, we shouldn't need a runtime function call to initialize it! This patch makes the MediaTime constructor constexpr so that we don't need runtime initialization for static MediaTime variables. This allows us to declare them outside functions and enables the compiler to generate code without guard variables when static MediaTime variables are declared inside functions. A test has been added accessing a global const static MediaTime. The build should not produce any error stating the need for a global constructor.