Constructor called in one window that came from another window isn't finding the prototype WPT expects it to

[pshaughn]

WebIDL/ecmascript-binding/constructors.html fails various cases with messages like expected object "[object DOMParserPrototype]" but got object "[object DOMParserPrototype]", the problem being that it's seeing the prototype that belongs to one global as opposed to another.

https://wpt.fyi/results/WebIDL/ecmascript-binding/constructors.html?label=experimental&label=master&aligned Servo is not alone here; WPT's specific ideas about which prototype should be used when are not currently shared among non-Firefox browsers.

[pshaughn]

#25039 might share a cause, but that one is seeing constructors equal when they should be unequal and this one is the other way around.