Change mActiveTrack to mActiveTracks vector

The size of mActiveTracks is still limited to 1 for now.

Change-Id: Ia6b06b25d8c4709f087110ae29c589999407a2a2
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index d31009e..6b81c38 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -938,9 +938,11 @@
 
             AudioStreamIn                       *mInput;
             SortedVector < sp<RecordTrack> >    mTracks;
-            // mActiveTrack has dual roles:  it indicates the current active track, and
+            // mActiveTracks has dual roles:  it indicates the current active track(s), and
             // is used together with mStartStopCond to indicate start()/stop() progress
-            sp<RecordTrack>                     mActiveTrack;
+            SortedVector< sp<RecordTrack> >     mActiveTracks;
+            // generation counter for mActiveTracks
+            int                                 mActiveTracksGen;
             Condition                           mStartStopCond;
 
             // updated by RecordThread::readInputParameters()