GitLab

This CL:
* Adds some debug logging to the keyboard code (DVLOG).
* Cleans up ChromeKeyboardBoundsObserver and refactors
  ShouldWindowOverscroll to not be dependent on Ash.
* Removes Ash and KeyboardController dependencies from browser tests.

These changes are in preparation for enabling the virtual keyboard in
SingleProcessMash and should have no impact on existing tests or
behavior.

Bug: 843332
Change-Id: I8954b4640c39e670350adae776fe14b079e37f36
Reviewed-on: https://chromium-review.googlesource.com/c/1343557
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Reviewed-by: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609895}