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This CL adds audio detailed view (audio settings) to UnifiedSystemTray.
Audio settings is only accessible when there are multiple audio inputs
or outputs.

TEST=manual
BUG=847770

Change-Id: Ifee6be242c9c89bdb8012f3a6c905fca042aa1c6
Reviewed-on: https://chromium-review.googlesource.com/1098871Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567184}