SoundPool monitors AppOps for OP_PLAY_AUDIO

Fix performance regression in SoundPool by not checking SoundPool
  can play audio everytime it's about to play.
Instead check for permission in constructor and register a listener
  for changes on OP_PLAY_AUDIO.

Bug 20018833

Change-Id: I4e7a633d23b98653a149681d18a387cd560efe4d