The Java message object may be held by user-provided message handlers beyond
the lifetime of the raw blink::PlatformMessage and its data buffer

This type appears to be missing in older Mac SDKs.

* 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

FragmentActivity is required for plugins that use auto managed Google APIs, such as Google Sign-In. Requires flutter/flutter#9036 to land so that gradle builds include FragmentActivity.

We already have a //third_party/gtest that we use for our testing.

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.

Fixes https://github.com/flutter/flutter/issues/8968

Fixes https://github.com/flutter/flutter/issues/8809

Updating SetListener to SetEventListener which comes with a new SetHitViewTester

gn check does not run a C preprocessor, so it cannot understand that a
particular include does not apply to a particular build configuration.

See https://github.com/flutter/flutter/issues/8929

Fixes https://github.com/flutter/flutter/issues/8115