measure blocked layout queries
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- [x] These changes fix#19797
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No longer needed now that the case-sensitive flag for attributes selectors is
supported.
Update user-agent CSS sheet to use the standard flag.
Fixes#23227
Reduce unnecessary iframe size messages
This should be an improvement on pages that include iframes, since we currently run two layout jobs for every display-oriented layout request. When building the display list, we send a message to the constellation that includes the sizes of all iframes present, and the constellation sends resize messages to the script thread. This results in a mouse event on the outer page causing all frames to be re-laid out even if no changes occurred to the iframe sizes, which is ridiculous.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#22394
- [x] These changes do not require tests because there is no way to test this internal detail.
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Added comment about layout thread exit workflow
Comments
Regarding clarify layout-thread exit workflow (Specifically:when will a Exit message be received )
Added comment about layout thread exit workflow
Instead of per-document. This also allows to reuse this thread-pool if needed
for other stuff, like parallel CSS parsing (#22478), and to share more code with
Gecko, which is always nice.
