Whenever a stream type is muted, the progress bar in volume panel
is at 0.
If a stream is muted by ringer mode and does not control ringer mode,
the progress bar is disabled.
Pressing VOL- when in vibrate or silent mode resets the last audible
volume of ringtone stream (music strem on tablets) to 0.
VolumePanel implementation:
- Always prefer AudioManager APIs over AudioService APIs when available on both.
- Do not use AudioManager.shouldVibrate() (deprecated).
Change-Id: I57fcb19ada4e8d729b6b41d668496562ebe340c3
8c78752f2b