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- When ChromeVox is enabled, launcher state transitions to peeking or
  fullscreen are now announced.
- This fix also removes the ability to focus on the expand arrow while
  in fullscreen.

Bug: 779687
Change-Id: I942737bed53c258272aaea1a379cb7dd4053f605
Reviewed-on: https://chromium-review.googlesource.com/c/1423741Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Reviewed-by: Weidong Guo <weidongg@chromium.org>
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625756}