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In this CL, we observe the following events:
- A window being recorded gets closed.
- A display being fullscreen-recorded gets disconnected.
- System shutting down.

The above events end video recording.

BUG=1142994
TEST=Added new tests.

Change-Id: I5f03448d1399297e9589d561d9854b3c8cffc0f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2516239
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823831}