added dom obj counting to decide sequential/parallel layout (#10110)
This is a rebased version of #11713
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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#10110 (github issue number if applicable).
- [X] There are no tests for these changes because it's an optimization with no visible behavioral changes
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Reimplement scrolling to fragments
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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#13736, #10753 (github issue number if applicable).
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This reimplemntation of the feature uses ScrollRootIds to scroll
particular scrollable areas of the page.
Fixes#13736.
Fixes#10753.
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Layers were a feature of the legacy drawing path. If we re-add them at
some point, it probably makes more sense to make them a product of
display list inspection.
This change also remove a bunch of dead painting code.
This removes paint threads, rust-layers dependency, and changes
optional webrender types to be required.
The use_webrender option has been removed, however I've left
the "-w" command line option in place so that wpt
runner can continue to pass that. Once it's removed from there
we can also remove the -w option.
Once this stage is complete, it should be fine to change the
display list building code to generate webrender display
lists directly and avoid the conversion step.
