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.cc

@@ -0,0 +1,27 @@
+/*
+ *  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.
+ */
+
+#if defined(_WIN32)
+    #include <windows.h>
+    #include "critical_section_windows.h"
+#else
+    #include "critical_section_posix.h"
+#endif
+
+namespace webrtc {
+CriticalSectionWrapper* CriticalSectionWrapper::CreateCriticalSection()
+{
+#ifdef _WIN32
+    return new CriticalSectionWindows();
+#else
+    return new CriticalSectionPosix();
+#endif
+}
+} // namespace webrtc