Allow media track switching.

media/base/audio_renderer.h

Index: media/base/audio_renderer.h
diff --git a/media/base/audio_renderer.h b/media/base/audio_renderer.h
index 48cf7b7266cb5dc779c4175bf3db783227b84967..0bd368d3303276770f82de959439df4b96f7d704 100644
--- a/media/base/audio_renderer.h
+++ b/media/base/audio_renderer.h
@@ -32,6 +32,11 @@ class MEDIA_EXPORT AudioRenderer {
   //
   // |cdm_context| can be used to handle encrypted streams. May be null if the
   // stream is not encrypted.
+  //
+  // AudioRenderer may be reinitialized for playback of a different demuxer
+  // stream by calling Initialize again when the renderer is in a flushed
+  // state (i.e. after Flush call, but before StartPlaying). This is used for
+  // media track switching.
   virtual void Initialize(DemuxerStream* stream,
                           CdmContext* cdm_context,
                           RendererClient* client,