Firefox returns JS functions from document.createElement

[DartBot]

This issue was originally filed by ngeoffray@google.com

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After debugging html/tests/element_types_test, I found that:

document.createElement("object")

Returns a JS function, that prints to [object HTMLObjectElement]

document.createElement("embed")

Returns a JS function, that prints to [object HTMLEmbedElement]

[blois]

Yes, it's ugly. We have a supported flag on these types which indicate whether or not they're supported and right now we just consider EmbedElement and ObjectElement to be unsupported on FF.

There was a bug in the test which was masking the supported failure for ObjectElement so it was being annotated as supported on FF, I fixed the test and updated the annotation.

Right now our plan has been to keep these types unsupported on FF.

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Set owner to @blois.
Added Accepted label.

[blois]

Added Fixed label.