Stylo: Add support for grid-template-{rows,columns}
This has the implementation of grid's `<track-list>` nightmare.
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stylo: Don't mess up traversal drivers.
Right now it's harmless, but it trips assertions that are nice to have, just in
case it stops being the case.
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Check snapshot id/class flags before looking for those attributes.
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Most elements don't have classes or IDs.
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Not headless by default
Without this, initializing Servo without using the command line (when embedded) requires to explicitly set `opts.headless = false`, which is weird as it's the only option that needs to be changed.
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make gl context current on browser initialization
As explained in servo/webrender#1233, it's necessary to make the current gl context current when the browser is initialized, otherwise the wrong gl context might be used if another window is created before the initialization.
/cc @glennw
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Using TransformStyle::Preserve3D
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The changes were reviewed previously as a part of WR update PRs, but then we decided to move them out.
r? @emilio
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Fix containing block size for absolute root element
The root element doesn't have a containing block, so use the viewport size instead of `self.base.absolute_cb`.
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Implement Houdini worklets
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This PR implements the current draft Houdini Worklets specification (https://drafts.css-houdini.org/worklets/).
The implementation is intended to provide a responsive environment for worklet execution, and in particular to ensure that the primary worklet executor does not garbage collect, and does not block loading module code. The implementation does this by providing a thread pool, and performing GC and module loading in a backup thread, not in the primary thread.
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- [x] These changes fix#16206
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