Split off the current control block to separate file

Prepare for a new implementation of step() etc.

Change-Id: I268421976ba577aa1fb5d7015de5441c05861190
diff --git a/media/libmedia/Android.mk b/media/libmedia/Android.mk
index f2b6441..a35d562 100644
--- a/media/libmedia/Android.mk
+++ b/media/libmedia/Android.mk
@@ -13,6 +13,7 @@
 
 LOCAL_SRC_FILES:= \
     AudioTrack.cpp \
+    AudioTrackShared.cpp \
     IAudioFlinger.cpp \
     IAudioFlingerClient.cpp \
     IAudioTrack.cpp \