Before the introduction of the MODE_IN_COMMUNICATION audio mode,
"calls" were only made through telephony and the PhoneStateListener
was used to request and abandon audio focus as calls where started
and ended. VoIP applications do not cause phone state events to
be broadcast, and set the audio mode to MODE_IN_COMMUNICATION
directly. This change monitors mode changes to automatically
grab and abandon audio focus.
Change-Id: Ie9a4193e35ba8447764fac66a988959a93c4909f
2ade576148