Use multiple shared memory buffers cyclically for audio capture.

content/browser/renderer_host/media/audio_input_renderer_host.h

Index: content/browser/renderer_host/media/audio_input_renderer_host.h
===================================================================
--- content/browser/renderer_host/media/audio_input_renderer_host.h	(revision 186364)
+++ content/browser/renderer_host/media/audio_input_renderer_host.h	(working copy)
@@ -125,7 +125,8 @@
   void OnCreateStream(int stream_id,
                       const media::AudioParameters& params,
                       const std::string& device_id,
-                      bool automatic_gain_control);
+                      bool automatic_gain_control,
+                      int shared_memory_count);
 
   // Track that the data for the audio stream referenced by |stream_id| is
   // consumed by an entity in the render view referenced by |render_view_id|.