Replace more ObserverList with base::ObserverList.

media/base/user_input_monitor.h

Index: media/base/user_input_monitor.h
diff --git a/media/base/user_input_monitor.h b/media/base/user_input_monitor.h
index ab572694ed3351d3e1f648718640d4d76bab03b0..8016a009061bb8825f1ca93f687e772a669161be 100644
--- a/media/base/user_input_monitor.h
+++ b/media/base/user_input_monitor.h
@@ -33,7 +33,7 @@ class MEDIA_EXPORT UserInputMonitor {
    protected:
     virtual ~MouseEventListener() {}
   };
-  typedef ObserverListThreadSafe<UserInputMonitor::MouseEventListener>
+  typedef base::ObserverListThreadSafe<UserInputMonitor::MouseEventListener>
       MouseListenerList;
 
   UserInputMonitor();