Watchdog: add media.metrics

The media.metrics dump will show with an ANR, so to observe this,
one can force an ANR by stopping a key service
e.g. adb shell 'kill -STOP $(pgrep audioserver)'
and waiting a couple of minutes.

Test: adb bugreport
Bug: 71483452
Change-Id: Ie6fb2377eaecbb9e3c09f0e1b0a55c284fd4bc5f