Dartium: Objects in IFrames get wrapped, even if accessed through JSInterop

[alan-knight]

e.g. LibTest/html/IFrameElement/IFrameElement.created_A01_t01

[terrylucas]

class MyIFrameElement extends IFrameElement {
MyIFrameElement.created() : super.created();

void testit() {
print("In testit 222");
}
}

iframe_test() {
var ife;
var tag = 'my-iframe';
document.registerElement(tag, MyIFrameElement, extendsTag: 'iframe');

ife = document.createElement('iframe', 'my-iframe');
document.body.append(ife);

ife.testit();
print(ife);
}

[terrylucas]

See co19 issue dart-lang/co19#117 the test needs to change.