Refactor ring_buffer interface, add a feature and a test.

* Add a RingBuffer typedef.
* Add the ability to force a memcpy by passing a null ptr. In some cases,
  we know we want a memcpy. This allows us to skip a potential
  intermediate memcpy.
* Add a stress test.

Review URL: https://webrtc-codereview.appspot.com/1111004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3567 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/audio_processing/aecm/include/echo_control_mobile.h

@@ -11,7 +11,9 @@
 #ifndef WEBRTC_MODULES_AUDIO_PROCESSING_AECM_INCLUDE_ECHO_CONTROL_MOBILE_H_
 #define WEBRTC_MODULES_AUDIO_PROCESSING_AECM_INCLUDE_ECHO_CONTROL_MOBILE_H_
 
-#include "typedefs.h"
+#include <stdlib.h>
+
+#include "webrtc/typedefs.h"
 
 enum {
     AecmFalse = 0,