AudioTrackTest: added testGetTimestamp.

testGetTimestamp tests:
1. frames written by client (AudioTrack.write)
    >= frames seen by server (AudioTrack.getPlaybackHeadPosition)
    >= frames presented to output device (AudioTrack.getTimestamp)
2. The output frequency reported by AudioTrack.getTimestamp remains
   stable and lies in the same ballpark as the write frequency.

Bug: 12111220
Change-Id: I538d11ce300212a59877d399316f4404d469da99
1 file changed