Update AudioTrack docs for source sample rate
Update AudioTrack docs for source sample rate

Add "source" for sampling rate.
Add "initial" to constructor sample rate parameter.
Abbreviate Hertz to standard Hz.

Unrelated:
 - fix spelling typo
 - add comment to session ID parameter

Change-Id: I0902ba5d77ff21fc961f717c984f28255d5fe9b3

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base