Now with fewer lists.

Users of MaterialApp can provide an onLocaleChanged handler that will be
called to asynchronously fetch locale-specific data.  MaterialApp will
then instantiate a LocaleQuery that supplies the locale data to its
descendants.

We use a number of non-public APIs in the test package, which makes our
dependency quite fragile. This patch pins a specific, known-good version. We
should update to the lastest version in a follow-up patch.

This updates the Flutter tools to match the proposed new packaging of artifacts
in the engine release script.
* The GCS URL for artifacts is now gs://mojo/flutter/$revision/$platform
* Categories have been removed from the Artifact class
* All artifacts for a given platform now live in a zip file.  If an artifact
  is not present in the local cache, then the zip will be downloaded and
  extracted.

Note that darwin-x64 artifacts go through a different process that (for now)
continues to use the old format.

The current implementation is still pretty rudimentary.

Using local paths ensures that each package sees each other package at HEAD.

Move us to a version of sky_tools that doesn't hang when the tests crash.

sky_engine is now at 0.0.45
sky_services is now at 0.0.45
flx is now at 0.0.4
flutter is now at 0.0.15
flutter_sprites is now at 0.0.12

sky_engine is now at 0.0.44
sky_services is now at 0.0.44
flx is now at 0.0.3
flutter is now at 0.0.14
flutter_sprites is now at 0.0.11