* Roll Skia revision to 342977ced701d06df2b3d2eedd8b64aeae1eb5c5

* Updated license files

android_tools contains a toolchain that is specific to each host platform

Fixes https://github.com/flutter/flutter/issues/8969

The script keeps state in the objects representing the repository files,
and it also maintains a cache of licenses.  This state should be freshly
recreated for each component so data from previous components does not
leak through.

See https://github.com/flutter/flutter/issues/8106

New concepts: FlutterMessageChannel (basic message send/receive superseding existing FlutterView methods), FlutterMethodChannel (method invocation and event streams), pluggable codecs for messages and method calls: unencoded binary, string, json, and 'standard' flutter binary encoding.

This contains some fixes for Fuchsia and I'd like to keep the version
of Dart used in fuchsia and flutter builds consistent. Should have no
other impactful changes for Flutter.

I had added this initially as a means of making it easier to deal with OpenGL directly in Flow. However, we are moving away from dealing with the client rendering APIs directly. Instead, delegating everything to Skia. Besides, we only ever used this to log the GPU description in case of context setup failures. This has not proved to be useful so far. Also, having this in place is making it difficult to remove all dependencies on GL in Shell.

Merged iOS and Android font fallback mechanisms and push font discovery logic into skia

See issue flutter/flutter#8115

Picks up changes to include inlined frames and line numbers in AOT stack traces.

* [iOS] Ensure FlutterMain is called before interacting with the engine in any way.

* Licenses

* Roll Dart SDK to b43da048c31a16b9993de1536406ed014ef73ffd

* Update licenses.golden for Dart SDK

* Update LICENSE for sky_engine

The first 23 lines of the BoringSSL license contain informational text
including Buganizer issue numbers that is not part of the license text
itself.

* Add OpenSSL as supported licence type

Adds special handling for the OpenSSL licensed files under BoringSSL.
Specifically, some of the ARM assembly files in the latest Dart SDK are
dual-licensed with OpenSSL.

* Support blocks that ref by type with no copyright

The upcoming Dart SDK includes files (e.g., sha256-armv4.S) with a block
that specifies teh code is dual-licenced under OpenSSL, but doesn't
include a copyright date of its own.

* Roll Dart SDK to 3a422bceb76d6155cab0c728b68f2badad8ff0e9

* Update licences.golden for latest Dart SDK

* This allows the tests to add their own FLX files but still use consistent fonts.
* The test fonts are only embedded on the desktop test shells. The option is not available on mobile platforms.
* Right now, all fonts will resolve to the test font. If we want tests to be able to use the fonts they embed in FLX files but use the test font for platform fallbacks, we will need to add font selector fallbacks. I can do this in an another patch. So far, there are no users of this functionality.

Fixes https://github.com/flutter/flutter/issues/7182

* Test that licenses are valid.

* Move license script from flutter/buildroot to flutter/engine