chromium/third_party/blink/web_tests/http/tests/misc/frame-access-during-load.html

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<p>This test verifies that  accessing a frame's document while it is still loading does not prevent the load, but can
access at least a temporary empty document.</p>
<iframe frameborder=0 height=40 id="frame1" src="resources/success.html"></iframe><br>
<iframe frameborder=0 height=40 id="frame2" src="resources/success.html"></iframe><br>
<script>
document.write(frames[0].document);
document.write('<br>');
document.write(document.getElementById("frame2").contentDocument);
</script>
<p>If this test passes, you should see SUCCESS twice, followed by [object HTMLDocument] twice.

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