Add Element.style support for stylo
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This is the Servo side change of [bug 1294299](https://bugzilla.mozilla.org/show_bug.cgi?id=1294299) which has been reviewed by @heycam, @emilio, and @SimonSapin.
This should not be merged until the Gecko side change gets merged into mozilla-central.
r? @heycam
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Implement CSS filter for Stylo
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This patch is part of https://bugzilla.mozilla.org/show_bug.cgi?id=1310117
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It is called nsstring_vendor since libgkrust already depends on nsstring, and
we can't have two crates with the same name in-tree. We can't directly depend
on the in-tree one since this will stop independent `./mach build-geckolib` builds from working.
MozReview-Commit-ID: CR4tHgzXWFZ
Fix return types of Owned<T>::into_box Gecko sugar types.
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We're not transmuting to the right type. The only current use of `into_box` is to drop a `PerDocumentStyleData`, so we weren't accidentally doing anything terribly bad, just not calling the `Drop` impl for that type.
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avoid initializing image layers after repeat/origin values have already been written
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@bors-servo r=manishearth
given in https://bugzilla.mozilla.org/show_bug.cgi?id=1309081
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