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- Change the fullscreen string to be consistent in image capture and
video capture scenarios
- Click/Tap anywhere can start fullscreen capture

TODO:
- cursor change will be done in a following up cl.

Bug: 1142937
Change-Id: Ife37530245cbc48f8c75be0756d4d45157aac874
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536081Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827181}