Constellation manages script thread lifetime
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Yet another step towards fixing #633...
At the moment, script threads are responsible for killing themselves when they have no more pipelines to manage. This is fine right now, because script threads have a root pipeline: once it is closed, everything is closed. It's not fine once we fix#633 because there's a race condition where the constellation could kill the last pipeline in a script thread, then open a new one in the same script thread.
We can't have the constellation block on the script thread, waiting to make sure a pipeline is created, since this could introduce deadlock. The easiest solution is to have the constellation manage the script thread lifetime: when the constellation discovers that a script thread is not managing any live pipelines, it closes the script thread, and updates its own state.
Most of the commits are from #14013, its just "Script thread lifetime is now managed by the constellation." (9ac6e4d2ba) that's new.
cc @jdm @ConnorGBrewster
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Script thread with no root document
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This PR removes the single root document from the script thread, and replaces it by a lookup table from `PipelineId`s to `Document`s. This is needed if we're going to share script threads, as per #633.
The last commit is the one that matters, the ones before are #13646.
cc @jdm @Ms2ger @ConnorGBrewster
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#13875 - Implement parsing/serialization for font-size-adjust.
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Implement parsing/serialization for font-size-adjust.
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Webbluetooth Async behaviour
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Note: depends on https://github.com/servo/servo/pull/13612
The current WBT communication is synchronous. With this, it should work properly (except the disconnect function, which will need some more work, because the current implementation differ from the spec).
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Rename media_queries::MediaQueryList to MediaList
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`MediaList` is the name of the interface for "collection of media queries" used in [CSSOM spec](https://drafts.csswg.org/cssom/#the-medialist-interface), `MediaQueryList` happens to mean something different in [CSSOM View spec](https://drafts.csswg.org/cssom-view/#the-mediaquerylist-interface), which also leads to naming conflict in dom code. So I think it's better renaming it to `MediaList`.
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Define "display list"
Fix a TODO in the Glossary.
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Don't promote all scrollable regions to stacking contexts
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Don't promote all scrollable regions to stacking contexts
Instead annotate all flows with their owning ScrollRoots. When
processing the display list items into a flattened display list, we add
PushScrollRoot and PopScrollRoot to signal when scrolling regions start
and end. It is possible for content from different scrolling regions to
intersect and when they do, the stack of scrolling regions is
duplicated. When these duplicated scrolling regions stacks reach
WebRender, it will scroll them in tandem.
The PushScrollRoot and PopScrollRoot items are currently represented as
StackingContexts in WebRender, but eventually these will be replaced
with special WebRender display items.
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incremental restyle: Use more concrete types in the style system
We need to hang both snapshots and restyle damage off of ElementData, and so we need them to be concrete to avoid infecting ElementData with the trait hierarchy.
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