Bug 325133

Setting size or multiple on a <select> whose base appearance picker is open leaves the picker showing. The element picks up the list box rules from selectMultipleAndListBox.css, so it lays out a correctly sized but empty list box, while its options stay slotted in the still-showing popover and render in the top layer above the page. :open keeps matching a list box. Steps: 1. Enable Enhanced HTML select element for multiple and list box. 2. <select style="appearance: base-select"> with a few options, and ::picker(select) { appearance: base-select }. 3. Click it to open the picker. 4. From the console, select.multiple = true. No size attribute is needed: preferredSize() goes 1 to 4 through the m_multiple ? 4 : 1 fallback, so supportsPickerPseudoElement() becomes false while the popover is still showing. Nothing closes the picker on this transition: - attributeChanged() for sizeAttr invalidates style and renderers, calls setRecalcListItems() and invalidateButtonText(), and never touches the popover. - parseMultipleAttribute() computes oldBoxType != boxType() and uses it only to invalidate style. - Both queuePickerCloseForAppearanceChange() call sites key on usedAppearance() flipping away from Base, which a size or multiple change does not do. pickOrToggleOption()'s hidePickerPopoverElement() recovers the select.size = N variant, but it sits behind if (!m_multiple), so it never fires for the multiple case. Popover light dismiss recovers both, but not until the user clicks away. Suggested fix: key on supportsPickerPseudoElement() going false across the attribute change rather than on the attribute differing, so size 4 to 5 does nothing and 1 to 2 closes. Prefer the queued close to calling hidePickerPopoverElement() synchronously, since attributeChanged() can run under ScriptDisallowedScope during parsing, which means parameterizing the console message that currently names the appearance property.