Replace glutin by winit + surfman 0.2
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This PR updates surfman to 0.2, and replaces glutin with winit+surfman.
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Always upgrade existing weak child references in the rule tree
Just because we didn't find a child when read-locking a node children list
doesn't mean it still won't exist while we wait to upgrade the read lock
into a write lock to create the child.
Eliminate `AnimationFrame`
This intermediate data structure doesn't really buy us anything and is a
bit confusing.
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Just because we didn't find a child when read-locking a node children list
doesn't mean it still won't exist while we wait to upgrade the read lock
into a write lock to create the child.
This implements the easy / straight-forward parts of the :where / :is
selectors.
The biggest missing piece is to handle properly invalidation when there
are combinators present inside the :where. That's the hard part of this,
actually.
But this is probably worth landing in the interim. This fixes some of
the visitors that were easy to fix.
Differential Revision: https://phabricator.services.mozilla.com/D70788
Refactor ImageCache::find_image_or_metadata -> ImageCache::{get_image, track_image}
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Updated the `ImageCache` trait to replace `find_image_or_metadata` with two new functions `track_image` and `get_image`, as well as a new enum (`ImageCacheResult`).
As a result, I was able to refactor the functions that previously called `find_image_or_metadata` pretty cleanly. For a list of these functions, please see the commit information.
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