Update common_audio

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Moved src/ to webrtc/ to easily diff against the third_party/webrtc
   in the chromium tree

 * ARM/NEON/MIPS support is not yet hooked up

 * Tests have not been copied

webrtc/system_wrappers/source/critical_section_posix.h

@@ -0,0 +1,35 @@
+/*
+ *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_SYSTEM_WRAPPERS_SOURCE_CRITICAL_SECTION_POSIX_H_
+#define WEBRTC_SYSTEM_WRAPPERS_SOURCE_CRITICAL_SECTION_POSIX_H_
+
+#include "critical_section_wrapper.h"
+
+#include <pthread.h>
+
+namespace webrtc {
+class CriticalSectionPosix : public CriticalSectionWrapper
+{
+public:
+    CriticalSectionPosix();
+
+    virtual ~CriticalSectionPosix();
+
+    virtual void Enter();
+    virtual void Leave();
+
+private:
+    pthread_mutex_t _mutex;
+    friend class ConditionVariablePosix;
+};
+} // namespace webrtc
+
+#endif // WEBRTC_SYSTEM_WRAPPERS_SOURCE_CRITICAL_SECTION_POSIX_H_