Enable implicit signalling for HE AAC v1 & v2 in ADTS.

media/renderers/audio_renderer_impl.h

Index: media/renderers/audio_renderer_impl.h
diff --git a/media/renderers/audio_renderer_impl.h b/media/renderers/audio_renderer_impl.h
index 8c6df1e3e90ae82f71dae76ce240601b5eeab4e0..a16a861193b7a50d86e8525e2377be63b39a8072 100644
--- a/media/renderers/audio_renderer_impl.h
+++ b/media/renderers/audio_renderer_impl.h
@@ -232,6 +232,10 @@ class MEDIA_EXPORT AudioRendererImpl
   // HandleSplicerBuffer_Locked() call.
   int64_t last_audio_memory_usage_;
 
+  // Sample rate of the last decoded audio buffer. Allows for detection of
+  // sample rate changes due to implicit AAC configuration change.
+  int last_decoded_sample_rate_;
+
   // After Initialize() has completed, all variables below must be accessed
   // under |lock_|. ------------------------------------------------------------
   base::Lock lock_;