This reverts commit 74662ab695238af0e7402f41c4bf9ad862bd37d2.
This should land after https://github.com/flutter/engine/pull/6442
* Add pragma vm:entry-point
Otherwise, an object may be both null and an instance of EnginieLayer at
the same time in Dart.
To make the PR minimal, we currently only share the engine layer when `pushPhysicalShape` (for Fuchsia) or `pushOffset` (for `RepaintBoundary` and `Opacity`) are called. They should be sufficient for our short-term perf goal. In the future, we can incrementally share more engine layers with the framework.
https://github.com/flutter/flutter/issues/21756
We push a bit up the tree during preroll to learn whether there system
composited layers below each layer. During update scene, we squash down
to paint tasks, which we execute after publishing the new scene.
Instead, make Layer::Paint take a new PaintContext that has just exactly
the state that it needs, mirroring PrerollContext. Also, rename
PaintContext to CompositorContext because it holds the context for the
whole compositor.
Previously we just dropped child scenes on the floor. Now we upload them
to Mozart. However, we just draw them on top of all the other content
and don't apply any clips or blends.
