This reverts commit cfc2b0cd.

The include paths for GL headers in mojo/public are busted

This reverts commit 92fdf25d.

This breaks the android x86 build:

gn gen --check in out/android_debug_x64
ERROR at //mojo/public/tools/BUILD.gn:59:9: Assertion failed.
        assert(current_cpu == "arm",
        ^-----
Only arm version prebuilt netowrk_service.mojo is available.
step returned non-zero exit code: 1

* Namespaces have been updated to reflect the move from //flutter/sky/shell to //flutter/shell.
* shell/BUILD.gn file has been split into smaller GN files for each subcomponent of the shell (common, GPU, diagnostic, testing).
* GN dependencies have been rewritten to stop exposing common shell dependencies as public. Duplicates have also been removed.
* GPU subcomponent has been updated make it more suitable for Vulkan integration.
* The GLFW backend has been resurrected.

Originally, this was a step that had to be carried out manually. Presumably because we did not want developers to download the Android SDK and NDK if they were not targetting Android. In practice, this is rarely the case. Even the buildbots unconditionally run the script (though they don’t need Android artifacts on the Mac since there is no Mac to Android builder).

This removes another //base dependency and will let us reuse this code
on Fuchsia.

Pulls in fixes related to incremental builds of Dart sources that end up in the snapshotter.

This is now the canonical location of the Mojo public SDK.

All that's left is two task runners, which should be statics somewhere.

There are now three ways to start Dart applications:

1) From a precompiled snapshot
2) From a snapshot
3) From source

When loading from source, we no longer use the complex data pipe /
dependency catcher mechanism. Instead, we just load the source
synchronously from the file system. This is appropriate because running
from source is used only during development and not during production.

The previous design was built assuming we would want to run from source
over the network, which meant we needed to be able to load source
asynchronously over a high latency channel.

Add an association between FlutterViews and Dart Isolates to the PlatformView service protocol support (#2886)

* Update to mojo ba13534f2b2af27a1d73e176f7406dbab25f8e14

* Fix build for updated mojo

* Fix android build. Undo some of the mojo roll.

* Fix iOS build.

This removes most (all?) of our dependency on base::RefCountedThreadSafe.