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Since we can't have more than one recording at a time, we should
disabled the video recording toggle button when the capture mode
session starts while recording is in progress.

BUG=1160343
TEST=Manually, added a new test.

Change-Id: Ib6b169c584b1fdf84926995a94fa07000be66c48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2601856Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839150}