DataSource: Remove global variables in DataSource related to sniff

Removed global variables related to sniff, and added Sniffer class
to implement the sniff functionality with non-static members.

CRs-Fixed: 567753
Change-Id: I35c331e2415753aa207c6f02e5e749a97f51fa90
libstagefright: Fix for FPS drop issue during A-V playback.

Issues:
-The AAC decoder was not updating the timestamp when EOS is reached.
-Logic to smoothen the real time update in AudioPlayer uses system
 time. This introduces corrupt timestamp during EOS.

Fix:
-Update the timestamp in AAC decoder when EOS is reached.
-Extrapolate realtime using system time in AudioPlayer when EOS is
 reached. Cap the value to realtime if  extrapolated time becomes
 greater than realtime.

CRs-Fixed: 384183 515066
Change-Id: Ice54501436431d2527fcd3d710d65d9732fcffdd