audioflinger: implement getTimestamp() for offloaded tracks

Bug: 9587132.
Change-Id: Ie9d5f4cca96306d08bc9a2dbd6edd8953096702d
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index 3fe470c..f13cb54 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -466,6 +466,8 @@
                 // Return's the HAL's frame count i.e. fast mixer buffer size.
                 size_t      frameCountHAL() const { return mFrameCount; }
 
+                status_t         getTimestamp_l(AudioTimestamp& timestamp);
+
 protected:
     // updated by readOutputParameters()
     size_t                          mNormalFrameCount;  // normal mixer and effects