chromeos: reset old capture client when capture changes

With mus clients there is a CaptureClient per top-level. When a new top-level
requests capture, the old one has to be expliclity told it lost capture,
otherwise state is never updated.

BUG=933102
TEST=covered by test

Change-Id: Ibae7b2aaab4e97bf08877f1e8853d0c061aa174c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525418
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641216}
3 files changed