GitLab

This enables the views version of the message_center, in preparation
for removing the Cocoa implementation.

Fixes:
- Use an EventGenerator in tests, rather than manually synthesizing
  events.
- NotificationInputContainerMD::HandleKeyEvent() now explicitly clears
  the text input field when handling VKEY_RETURN, as the test expects
  this.
- Disabling notifications is no longer handled in
  NotificationViewMD::ButtonPressed(), since it wasn't the button
  Listener for the block_all_button_ (the
  NotificationControlButtonsView is). Disabling is now handled in
  ToggleInlineSettings() instead.
- The SlideOut tests are disabled on Mac because the test framework
  doesn't support synthesizing gesture scroll events.

Bug: 739386
Change-Id: Id841779233662111f52d491ba78e5315422003b4
Reviewed-on: https://chromium-review.googlesource.com/c/1341091
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609514}