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.cc

@@ -0,0 +1,38 @@
+/*
+ *  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.
+ */
+
+#include "critical_section_posix.h"
+
+namespace webrtc {
+CriticalSectionPosix::CriticalSectionPosix()
+{
+    pthread_mutexattr_t attr;
+    pthread_mutexattr_init(&attr);
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+    pthread_mutex_init(&_mutex, &attr);
+}
+
+CriticalSectionPosix::~CriticalSectionPosix()
+{
+    pthread_mutex_destroy(&_mutex);
+}
+
+void
+CriticalSectionPosix::Enter()
+{
+    pthread_mutex_lock(&_mutex);
+}
+
+void
+CriticalSectionPosix::Leave()
+{
+    pthread_mutex_unlock(&_mutex);
+}
+} // namespace webrtc