Update webrender
These changes reflect changes in webrender's API that make RenderApiSender and RenderApi objects more challenging to share. This PR moves us to a model where:
* the compositor owns the main RenderApi object
* other threads that need to create transactions or manipulate fonts proxy those operations to the compositor (script/layout use IPC, while other threads use non-IPC channels)
* the webgl thread owns its own independent RenderApi
There are a few canvas2d-related dependencies that haven't updated, but they
only use euclid internally so that's not blocking landing the rest of the
changes.
Given the size of this patch, I think it's useful to get this landed as-is.
Remove unused code (1/N)
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First PR in a series of PRs to remove unused/dead code from servo, powered by an (upcoming) tool of mine. Please take a look and tell me if you want to keep something.
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Ensure transparent hit test region is sized and positioned correctly.
This addresses some edge cases that were missed by #22156. Specifically, in some cases the transparent region was being placed in the display list in front of the scrollable content, rather than behind it, and the size of the region did not account for parent stacking context.
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- [x] `./mach build -d` does not report any errors
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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] 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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