Change debug assertions to specific ones
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style: Move content property out of mako.
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r? emilio
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style: Don't serialize default values of the font shorthand.
This makes us consistent with the old style system and Blink / WebKit.
Not adding a test because shorthands serialization is a mess... :(
Anyway, nothing like fixing bugs by removing code.
Bug: 1436031
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Previously anything with the wrong stretch/italicness was considered
equally bad. Now we consider the wrong weight to be least bad, wrong
boldness of intermediate badness, and wrong itallicness to be most
bad.
The current implementation for boldness assumes that if Freetype
claims a font is not bold then it must have normal weight. However
fonts with lighter-than-normal weight are not claimed to be bold.
Therefore we get rid of this check.
This makes us consistent with the old style system and Blink / WebKit.
Not adding a test because shorthands serialization is a mess... :(
Anyway, nothing like fixing bugs by removing code.
Bug: 1436031
Change Offset_to_text_point function and add unit tests
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- [x] These changes fix#18613.
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- [x] Added unit tests and web platform tests
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Update WebRender
This allows servo to use the ExternalScrollId API from WebRender fixing
some issues related to duplicate scroll root ids.
Fixes#17176.
Fixes#19287.
Fixes#19648.
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- [ ] These changes fix#17176, #19287, and #19648.
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- [ ] These changes do not require tests because _____
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This allows servo to use the ExternalScrollId API from WebRender fixing
some issues related to duplicate scroll root ids.
Fixes#17176.
Fixes#19287.
Fixes#19648.
We first check that the discriminants are equal, then we pattern match only
on `*self` and use `PropertyDeclarationVariantRepr` to look into `other` directly.