Add TRACK_FAST for IAudioFlinger::createTrack

Currently not implemented by client or server

Change-Id: Ib11dda57db3eeb871bcc7b546e340078776875f5

Author: gkasten

include/media/IAudioFlinger.h

@@ -45,8 +45,9 @@ class IAudioFlinger : public IInterface
 
     // or-able bits shared by createTrack and openRecord, but not all combinations make sense
     enum {
-        TRACK_DEFAULT = 0,
-        TRACK_TIMED   = 1,
+        TRACK_DEFAULT = 0,  // client requests a default AudioTrack
+        TRACK_TIMED   = 1,  // client requests a TimedAudioTrack
+        TRACK_FAST    = 2,  // client requests a fast AudioTrack
     };
     typedef uint32_t track_flags_t;