[frameworks/av] : added .mov extension

- while scanning the a/v files in sdcard it takes the container
  format extension and checks for whether it supports or not.
  So added support for mov extension in StagefrightMediaScanner.

CRs-Fixed: 515036

Change-Id: I140a96cd535178b64b5d7c8bafe20eece2243953
libmediaplayerservice: Avoid writing silence for offload tracks

-Audio Sink writes silence to the track if size returned from AudioPlayer
 is zero and when there is no subsequent output.
-Avoid writing silence for offload tracks as decoders do not expected
 any raw data.

CRs-Fixed: 615468
Change-Id: I5044d514126c413f56971e80815f232298f9685c