AudioService maintains a stack of registered media button event
receivers.
This change modifies the broadcasters of ACTION_MEDIA_BUTTON intents
let AudioService directly handle the corresponding key event instead
of trapping the intent sent by PhoneWindowManager, KeyguardViewBase
and PhoneFallbackEventHandler.
Because the key event may be sent through a PendingIntent,
AudioService now also implements the OnFinished interface to be
notified when the event was consumed so it can release the wake
lock held if it was held when the key event needed to be sent
(see where PassHeadsetKey was instanciated in PhoneWindowManager).
Change-Id: I2e8614df94af9d54edbf714ef443cc372d21827a
c68022258e