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This change adds several metrics for the device picker in the Global
Media Controls dialog:

Media.GlobalMediaControls.NumberOfAvailableAudioDevices tracks the
number of audio devices displayed in the device picker UI each time it
is opened.

Media.GlobalMediaControls.DeviceSelectorAvailable tracks if the device
selector was available.

Media.GlobalMediaControls.DeviceSelectorOpened tracks if the device
selector was opened.

For details see the entries in histograms.xml

Bug: 1096257
Change-Id: Ia67b919ee63330239ed5e4cd38c694142896417d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2393256
Commit-Queue: Noah Rose Ledesma <noahrose@google.com>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Auto-Submit: Noah Rose Ledesma <noahrose@google.com>
Cr-Commit-Position: refs/heads/master@{#806286}