Allow simulate_mouse_click to work with webrender.
Instead of dispatching to a specific layer, call the dispatch
functions for mouse (move) events that handle whether webrender
is enabled or not.
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Move PropertyDeclarationBlock into its own module.
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`properties.mako.rs` (its previous location) is a fairly big file.
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- [ ] These changes fix #__ (github issue number if applicable).
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Now that our Buildbot configuration is successfully able to read the
steps configuration from the main servo repo and run builds, sync the
steps in the servo tree to match the latest steps.yml from the saltfs
repo.
Run CSS Multicolumn tests automatically
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Implements the CSS multicolumn tests as outlined in issue #13587.
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- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#13587
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