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..455f0d4113815a1ec2f11ee9648c2bb5deaa9113 100644
--- a/chromecast/media/cma/base/decoder_buffer_base.h
+++ b/chromecast/media/cma/base/decoder_buffer_base.h
@@ -17,6 +17,11 @@ class DecryptConfig;
 namespace chromecast {
 namespace media {
 
+enum StreamId {
+  kPrimary = 0,
+  kSecondary
+};
+
 // DecoderBufferBase exposes only the properties of an audio/video buffer.
 // The way a DecoderBufferBase is created and organized in memory
 // is left as a detail of the implementation of derived classes.
@@ -25,6 +30,10 @@ class DecoderBufferBase
  public:
   DecoderBufferBase();
 
+  // Returns the stream id of this decoder buffer belonging to. it's optional
+  // and default value is kPrimary.
+  virtual StreamId stream_id() const = 0;
+
   // Returns the PTS of the frame.
   virtual base::TimeDelta timestamp() const = 0;