Use multiple shared memory buffers cyclically for audio capture.

media/audio/audio_device_thread.h

Index: media/audio/audio_device_thread.h
===================================================================
--- media/audio/audio_device_thread.h	(revision 186364)
+++ media/audio/audio_device_thread.h	(working copy)
@@ -38,7 +38,8 @@
    public:
     Callback(const AudioParameters& audio_parameters,
              base::SharedMemoryHandle memory,
-             int memory_length);
+             int memory_length,
+             int total_segments);
     virtual ~Callback();
 
     // One time initialization for the callback object on the audio thread.
@@ -61,6 +62,8 @@
 
     base::SharedMemory shared_memory_;
     const int memory_length_;
+    const int total_segments_;
+    int segment_length_;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Callback);