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

ppapi/proxy/media_stream_track_resource_base.h

Index: ppapi/proxy/media_stream_track_resource_base.h
diff --git a/ppapi/proxy/media_stream_track_resource_base.h b/ppapi/proxy/media_stream_track_resource_base.h
index 2dc2e36d11194da096f4a1aec43a7fe6601f6293..0e7e9cc2854d0265d370bf0067b8925dc761bb09 100644
--- a/ppapi/proxy/media_stream_track_resource_base.h
+++ b/ppapi/proxy/media_stream_track_resource_base.h
@@ -23,7 +23,7 @@ class PPAPI_PROXY_EXPORT MediaStreamTrackResourceBase
 
   MediaStreamTrackResourceBase(Connection connection, PP_Instance instance);
 
-  virtual ~MediaStreamTrackResourceBase();
+  ~MediaStreamTrackResourceBase() override;
 
   std::string id() const { return id_; }
 
@@ -42,8 +42,8 @@ class PPAPI_PROXY_EXPORT MediaStreamTrackResourceBase
   void SendEnqueueBufferMessageToHost(int32_t index);
 
   // PluginResource overrides:
-  virtual void OnReplyReceived(const ResourceMessageReplyParams& params,
-                               const IPC::Message& msg) override;
+  void OnReplyReceived(const ResourceMessageReplyParams& params,
+                       const IPC::Message& msg) override;
 
  private:
   // Message handlers: