Use sp<AudioTrack> instead of raw AudioTrack *

Change-Id: I7681b87da61e5602b20e55d16e96421fe03a558e
AudioTrack::obtainBuffer() and AudioRecord::obtainBuffer are now deprecated

As AudioGroup still uses these legacy APIs, it needs to explicitly
request the feature for it to be enabled.

Change-Id: I00aec5ff055842f914ca3e911f3d3b29e437ac6d
AudioRecord must be used as sp<> only

Bug: 9423855
Change-Id: Ib78b34a2b139cd0f0f8b119ad64e8d1e0d8140b2
Merge branch 'aosp44' into HEAD