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This CL modifies media tray bubble behavior such that when the dialog
is opened and all media stops playing, we will show an empty state
indicating there's no media playing instead of close the dialog
immediately.

Bug: 1134414
Change-Id: I3f0f2489da2189e6a71f74f6a00855d8b4a535f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444529Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Jazz Xu <jazzhsu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813279}