Allow media track switching.

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 f7915d31a607bdc512ac96704a1ddc7085c8d5cf..7f1e16d83f5222dd5df5739b343d3c08626b46a3 100644
--- a/media/renderers/audio_renderer_impl.h
+++ b/media/renderers/audio_renderer_impl.h
@@ -36,6 +36,7 @@
 #include "media/base/time_source.h"
 #include "media/filters/audio_renderer_algorithm.h"
 #include "media/filters/decoder_stream.h"
+#include "media/renderers/default_renderer_factory.h"
 
 namespace base {
 class SingleThreadTaskRunner;
@@ -62,7 +63,7 @@ class MEDIA_EXPORT AudioRendererImpl
   AudioRendererImpl(
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
       AudioRendererSink* sink,
-      ScopedVector<AudioDecoder> decoders,
+      const CreateAudioDecodersCB& create_audio_decoders_cb,
       const scoped_refptr<MediaLog>& media_log);
   ~AudioRendererImpl() override;
 
@@ -96,16 +97,18 @@ class MEDIA_EXPORT AudioRendererImpl
   // Important detail: being in kPlaying doesn't imply that audio is being
   // rendered. Rather, it means that the renderer is ready to go. The actual
   // rendering of audio is controlled via Start/StopRendering().
+  // Audio renderer can be reinitialized completely by calling Initialize again
+  // when it is in a kFlushed and stopped (StopTicking) state.

[xhwang, 2017/03/22 22:31:12]

Please update AudioRenderer interface documentation about when Initialize() can
be called.

[servolk, 2017/03/23 17:08:10]

Done.

   //
   //   kUninitialized
-  //         | Initialize()
-  //         |
-  //         V
-  //    kInitializing
-  //         | Decoders initialized
-  //         |
-  //         V            Decoders reset
-  //      kFlushed <------------------ kFlushing
+  //  +----> | Initialize()
+  //  |      |
+  //  |      V
+  //  | kInitializing
+  //  |      | Decoders initialized
+  //  |      |
+  //  |      V            Decoders reset
+  //  +-  kFlushed <------------------ kFlushing
   //         | StartPlaying()             ^
   //         |                            |
   //         |                            | Flush()
@@ -253,6 +256,8 @@ class MEDIA_EXPORT AudioRendererImpl
   // Simple state tracking variable.
   State state_;
 
+  CreateAudioDecodersCB create_audio_decoders_cb_;
+
   BufferingState buffering_state_;
 
   // Keep track of whether or not the sink is playing and whether we should be