Several /webidl/ecmascript-binding/window-named-properties-object.html
subtests, including the “[[GetOwnProperty]]” and “[[HasProperty]]”
subtests, expect iframe.contentWindow.Window.prototype[0] to return an
element with id “0”.
This commit makes the getOwnPropertyDescriptor trap accept property
keys that are integer indices, by converting them to a DOMString just
like we would for a property key that is a JSString.
Calling throw_type_error in the [[DefineOwnProperty]] trap (and
returning false) makes the internal method throw a TypeError, which
means both Object#defineProperty and Reflect#defineProperty will throw
a TypeError, but we actually want the latter to return false.
This commit makes the trap set ObjectOpResult to a TypeError (and
return true), making the internal method return false per the spec [1]
and in turn allowing Reflect#defineProperty to return false.
[1] https://webidl.spec.whatwg.org/#named-properties-object-defineownproperty
