GitLab

changes:
- make moving window between displays shortcuts "window needed", which
  means a11y alert "Alert Command unavailable. Press control-N to open
  a new window" is alerted when there is no window available.
- send a11y alert when there is actual window movement by shortcuts

Bug: 783058
Test: tested on device, working as expected; added test coverage.
Change-Id: I97a1fc2b771a10e1480a0a3dcf5107ae171e4f36
Reviewed-on: https://chromium-review.googlesource.com/767861
Commit-Queue: Qiang(Joe) Xu <warx@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516394}