Add thread safety to AudioManagerBase to protect access to the audio thread member variable.

media/audio/audio_low_latency_input_output_unittest.cc

Index: media/audio/audio_low_latency_input_output_unittest.cc
diff --git a/media/audio/audio_low_latency_input_output_unittest.cc b/media/audio/audio_low_latency_input_output_unittest.cc
index 683bf2b444d68822c3d4d6d3ed8c990f376a5425..7390e79c028a90d14ed64d7b7d0df49fc817504d 100644
--- a/media/audio/audio_low_latency_input_output_unittest.cc
+++ b/media/audio/audio_low_latency_input_output_unittest.cc
@@ -6,6 +6,7 @@
 #include "base/environment.h"
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/message_loop.h"
 #include "base/path_service.h"
 #include "base/synchronization/lock.h"
 #include "base/test/test_timeouts.h"
@@ -82,8 +83,8 @@ class MockAudioManager : public AudioManagerAnyPlatform {
 
   virtual ~MockAudioManager() {}
 
-  virtual MessageLoop* GetMessageLoop() OVERRIDE {
-    return MessageLoop::current();
+  virtual scoped_refptr<base::MessageLoopProxy> GetMessageLoop() OVERRIDE {
+    return MessageLoop::current()->message_loop_proxy();
   }
 
  private: