Use multiple shared memory buffers cyclically for audio capture.

content/common/media/audio_messages.h

Index: content/common/media/audio_messages.h
===================================================================
--- content/common/media/audio_messages.h	(revision 185810)
+++ content/common/media/audio_messages.h	(working copy)
@@ -48,21 +48,27 @@
 
 // Tell the renderer process that an audio input stream has been created.
 // The renderer process would be given a SyncSocket that it should read
-// from from then on.
+// from from then on. It is also given total number of shared memory handles.
 #if defined(OS_WIN)
-IPC_MESSAGE_CONTROL4(AudioInputMsg_NotifyStreamCreated,
+IPC_MESSAGE_CONTROL3(AudioInputMsg_NotifyStreamCreated,
                      int /* stream id */,
-                     base::SharedMemoryHandle /* handle */,
                      base::SyncSocket::Handle /* socket handle */,
-                     uint32 /* length */)
+                     uint32 /* total shared memory handles */)
+
 #else
-IPC_MESSAGE_CONTROL4(AudioInputMsg_NotifyStreamCreated,
+IPC_MESSAGE_CONTROL3(AudioInputMsg_NotifyStreamCreated,
                      int /* stream id */,
-                     base::SharedMemoryHandle /* handle */,
                      base::FileDescriptor /* socket handle */,
-                     uint32 /* length */)
+                     uint32 /* total shared memory handles */)
 #endif
 
+// Tell the renderer process that a shared memory handle has been created.
+IPC_MESSAGE_CONTROL4(AudioInputMsg_NotifySharedMemoryCreated,
+                     int /* stream id */,
+                     base::SharedMemoryHandle /* handle */,
+                     uint32 /* length */,
+                     uint32 /* handle index */)
+
 // Notification message sent from AudioRendererHost to renderer after an output
 // device change has occurred.
 IPC_MESSAGE_CONTROL3(AudioMsg_NotifyDeviceChanged,
@@ -97,11 +103,12 @@
                      media::AudioParameters /* params */)
 
 // Request that got sent to browser for creating an audio input stream
-IPC_MESSAGE_CONTROL4(AudioInputHostMsg_CreateStream,
+IPC_MESSAGE_CONTROL5(AudioInputHostMsg_CreateStream,
                      int /* stream_id */,
                      media::AudioParameters /* params */,
                      std::string /* device_id */,
-                     bool /* automatic_gain_control */)
+                     bool /* automatic_gain_control */,
+                     int /* shared memory count */)
 
 // Indicate that audio for a stream is produced by the specified render view.
 IPC_MESSAGE_CONTROL2(AudioHostMsg_AssociateStreamWithProducer,