GitLab

Add a simple WindowTree::SetHitTestMask impl and unit test.
Wire up the TouchHandleWindowTargeter, used in the KSV app, etc.
Clarify that the targeter only insets bounds, it does not extend them.

Bug: 872891
Test: KSV app text touches work as expected (modulo Issue 873743).
Change-Id: I4a1b79a8826a7e176ce3dafb29e1223ddd003966
Reviewed-on: https://chromium-review.googlesource.com/1171218Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583034}