Chromecast: Add stream id interface in DecoderBufferBase class

chromecast/media/cma/base/decoder_buffer_base.h

Index: chromecast/media/cma/base/decoder_buffer_base.h
diff --git a/chromecast/media/cma/base/decoder_buffer_base.h b/chromecast/media/cma/base/decoder_buffer_base.h
index 099b44d7a9e26a7f93afbe0a5204049424ba4365..a91c35f619cf58db5e6d398aff110412f35a7702 100644
--- a/chromecast/media/cma/base/decoder_buffer_base.h
+++ b/chromecast/media/cma/base/decoder_buffer_base.h
@@ -25,6 +25,10 @@ class DecoderBufferBase
  public:
   DecoderBufferBase();
 
+  // Returns the stream id of this decoder buffer belonging to. it's optional
+  // and the value is -1 if it's undefined.
+  virtual int stream_id() const = 0;
+
   // Returns the PTS of the frame.
   virtual base::TimeDelta timestamp() const = 0;