stagefright: Fix AV sync issue for cached audio sources

Non-HTTP sources may continue to fetch audio data after video has
already seen a seek request causing audio to run ahead. When video
sees a seek request, audio should pause, resuming once it too has
handled the seek request.

Change-Id: Iddbf3d79f29bbe8bcdb4b07338c4a00734acd8e2
AudioFlinger: Offload track transition fix

Trigger state changes in OffloadThread on adding a new offload track.

Bug: 12530661
Change-Id: I95b62764c7ac041d470702e86b951f812eb0e70f
audioflinger: Handle pause /resume in stopping state

-Pre-requisite:
 Perform seek on the clip. After seek the data remaining till EOS
 is little more than the driver and common block buffering.
-Framework state:
 Offload thread is waiting for signal from the HAL for a free
 buffer. Audio Player calls sink stop on reaching EOS. Audio
 track is waiting on obtain buffer for a free space in common
 block to send the last buffer. The track is moved to stopping
 state as input EOS is reached.
-Issue:
 Perform pause/ resume in this state(STOPPING), Audio playback
 does not resume.
-Fix
 Ensure resume is called in stopping state if frames ready is
 greater than zero.

Change-Id: I9268ab2a6cd1cc69a3ff23801f978f7a9f75a11b
AudioFlinger: Modify flush handling for offload path

Do not allow an offload track to directly control the offload thread
behavior. OffloadThread can check for any pending flush reporting
by its active tracks and decide to flush the HW or not.

Bug: 12530661
Change-Id: Ib33f023c942f6c091b618004136b153c38a6eef6