Update {virtual,override} to follow C++11 style in ppapi.

ppapi/shared_impl/media_stream_buffer_manager_unittest.cc

Index: ppapi/shared_impl/media_stream_buffer_manager_unittest.cc
diff --git a/ppapi/shared_impl/media_stream_buffer_manager_unittest.cc b/ppapi/shared_impl/media_stream_buffer_manager_unittest.cc
index a7f0ec794ef3a513cd0bc09dedf5a2a574118988..3db0117f59280310f2f7094a3ea02338e946e5fd 100644
--- a/ppapi/shared_impl/media_stream_buffer_manager_unittest.cc
+++ b/ppapi/shared_impl/media_stream_buffer_manager_unittest.cc
@@ -30,7 +30,7 @@ namespace ppapi {
 class MockDelegate : public MediaStreamBufferManager::Delegate {
  public:
   MockDelegate() : new_buffer_enqueue_counter_(0) {}
-  virtual void OnNewBufferEnqueued() override {
+  void OnNewBufferEnqueued() override {
     new_buffer_enqueue_counter_++;
   }