GitLab

We need to add touchscreen support to mustash where display and
input-device management happens in a different process from ash.
Decouple ash::TouchTransformerController from the rest of ash and move
to src/ui/display/ so it can be used with mus. This also decouples and
moves the accompanying tests.

The dependency on WindowTreeHostManager can't be broken so add
AshTouchTransformController which extends TouchTransformController and
listens for ash display configuration changes.

BUG=679747

Review-Url: https://codereview.chromium.org/2617043003
Cr-Commit-Position: refs/heads/master@{#443037}