Motown: Delay audio track completion of Prime requests until a packet arrives.

services/media/audio/audio_pipe.h

Index: services/media/audio/audio_pipe.h
diff --git a/services/media/audio/audio_pipe.h b/services/media/audio/audio_pipe.h
index 4a2b4fb9f4c4bfbd60e01ccc65d6ad4fadb252f8..d1fd7e2eb302380fcea47a8d35dfb59144e30e3e 100644
--- a/services/media/audio/audio_pipe.h
+++ b/services/media/audio/audio_pipe.h
@@ -81,6 +81,7 @@ class AudioPipe : public MediaPipeBase {
 
  protected:
   void OnPacketReceived(MediaPacketStatePtr state) override;
+  void OnPrimeRequested(const PrimeCallback& cbk) override;
   bool OnFlushRequested(const FlushCallback& cbk) override;
 
  private:
@@ -90,6 +91,8 @@ class AudioPipe : public MediaPipeBase {
   // State used for timestamp interpolation
   bool next_pts_known_ = 0;
   int64_t next_pts_;
+
+  PrimeCallback prime_callback_;
 };
 
 }  // namespace audio