Use multiple shared memory buffers cyclically for audio capture.

content/browser/renderer_host/media/audio_input_renderer_host.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // AudioInputRendererHost serves audio related requests from audio capturer
 // which lives inside the render process and provide access to audio hardware.
 //
 // Create stream sequence (AudioInputController = AIC):
 //
 // AudioInputHostMsg_CreateStream -> OnCreateStream -> AIC::CreateLowLatency ->
@@ skipping 107 matching lines @@
   // starts successfully, it will trigger OnDeviceStarted() callback.
   void OnStartDevice(int stream_id, int session_id);
 
   // Audio related IPC message handlers.
   // Creates an audio input stream with the specified format. If this call is
   // successful this object would keep an internal entry of the stream for the
   // required properties.
   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|.
   void OnAssociateStreamWithConsumer(int stream_id, int render_view_id);
 
   // Record the audio input stream referenced by |stream_id|.
   void OnRecordStream(int stream_id);
 
   // Close the audio stream referenced by |stream_id|.
   void OnCloseStream(int stream_id);
@@ skipping 54 matching lines @@
 
   // A map of session IDs to audio session sources.
   SessionEntryMap session_entries_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioInputRendererHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_INPUT_RENDERER_HOST_H_