* Update Skia revision to pull in GL native interface construction fixes on iOS.

Fixed in https://skia-review.googlesource.com/c/5212/

* Use the new image encoder API from Skia.

There's no reason to present offscreen child views to Mozart.

This interface has been replaced with HandleWaiter, which is the new hotness.

The same will be removed from buildroot as well.

- [x] Use Dart_GetLoadedLibraries which is available in product builds.

This file is identical (to the byte) to the LICENSE file in the same directory, and no file in this directory refers to it.

This requires an updated buildroot.

We need to compute the paint bounds of ChildViewLayers during Preroll.
Also, we need to allocate a BlendPtr before writing into it.

This also removes a reference to mojo_gni.

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.

* The lastchange hook wrote a file no one ever read.
* We don’t need binutils because we don’t use debug fission on Linux.
* We dont use eu-strip.

When we pipelined the drawing commands we caused UpdateScene to be called
before Preroll, which isn't allowed. Now we call Preroll, UpdateScene, and
Paint separately.

* Faster hash codes.

Mask the intermediate values when computing composite
hash codes.

* WIP

* WIP

* WIP

I updated the C++ and Dart sides but forgot to update the Java side.

Fixes https://github.com/flutter/flutter/issues/6891

These are implemented on macOS and Fuchsia.

Rather than hitting an assert in platform-independent code, we now trigger an
assert closer to the relevant code when the font provider is missing.

Previously, —unoptimized builds on Android would include debug symbols but still would be optimized. This killed the experience in the debugger on Android.