[Cast] Track audio queued in encoder; account for it in ShouldDropNextFrame().

media/cast/sender/audio_encoder.h

Index: media/cast/sender/audio_encoder.h
diff --git a/media/cast/sender/audio_encoder.h b/media/cast/sender/audio_encoder.h
index 5f080c6cb6a4c4e7ce567b862455324e4753cc7b..e0a3d8a5bafdb3aaa5b835f8674c59e21f002f34 100644
--- a/media/cast/sender/audio_encoder.h
+++ b/media/cast/sender/audio_encoder.h
@@ -20,7 +20,9 @@ namespace cast {
 
 class AudioEncoder {
  public:
-  typedef base::Callback<void(scoped_ptr<EncodedFrame>)>
+  // Callback to deliver each EncodedFrame, plus the number of audio samples
+  // skipped since the last frame.
+  typedef base::Callback<void(scoped_ptr<EncodedFrame>, int)>
       FrameEncodedCallback;
 
   AudioEncoder(const scoped_refptr<CastEnvironment>& cast_environment,
@@ -33,6 +35,8 @@ class AudioEncoder {
 
   CastInitializationStatus InitializationResult() const;
 
+  int GetSamplesPerFrame() const;
+
   void InsertAudio(scoped_ptr<AudioBus> audio_bus,
                    const base::TimeTicks& recorded_time);