Rule cache
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This adds a TLS-based cache reset styles structs keyed off rule nodes. Reviewed in https://bugzilla.mozilla.org/show_bug.cgi?id=1367635 by me and Emilio.
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This patch replaces the handwritten MallocSizeOf implementation for
PropertyDeclaration with a derived one, which gives much more thorough
measurement.
This requires (a) deriving MallocSizeOf for a *lot* of additional types (most
of which already have `derive(HeapSizeOf)` in Servo builds), and (b)
implementing MallocSizeOf for a few more types in the `malloc_size_of` crate.
These changes would significantly improve the reporting coverage for gmail if
it weren't for the fact that SpecifiedUrl isn't measured due to a lack of
clarity about its fields; that can be fixed as a follow-up once bug 1397971 has
landed.
Replace all uses of the style::stylearc alias with servo_arc.
The `stylearc` alias is left there temporarilly and will be removed completely in a later commit/PR where also `components/style/gecko/generated/structs_{debug|release}.rs` are re-generated (they still use the old alias).
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- [X] These changes fix#17768 (github issue number if applicable).
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This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17775)
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The alias is left there temporarilly and will be removed completely in a later commit where
also components/style/gecko/generated/structs_{debug|release}.rs are re-generated (they still
use the old alias).
