Added FormData Iterable
Implement FormData's iterator
Rebased from #13104.
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#13020
- [X] There are tests for these changes (It adds `./mach test-wpt tests/wpt/web-platform-tests/XMLHttpRequest/formdata-foreach.html`)
Notice: Our `FormData` is implemented by `HashMap` , which is different from [Gecko's array implementation](3c6ff93c8f/dom/base/FormData.h (L160)). So our `FormData`'s iterator order is different from Gecko's, as there is no way to keep our key's original insertion order.
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see #10947
Node::scroll_area should check if the element is potentially scrollable
Three tests use `document.scrollingElement` which was not supported at
the time of writing. They are, hence, expected to FAIL.
The last expected FAIL should be fixed by #10947.
Edited some comments, message texts.
indexed getter of form elements
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Added tests for cross-origin iframe parentage.
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Added (currently failing) tests for cross-origin iframe parentage.
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