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

ppapi/proxy/plugin_resource_callback.h

Index: ppapi/proxy/plugin_resource_callback.h
diff --git a/ppapi/proxy/plugin_resource_callback.h b/ppapi/proxy/plugin_resource_callback.h
index 9c443d8ae3908c741176b7923b3b2a0d7b766fb2..ecde1c2cd822d88b2267f7f2ff07e30d7427d9cb 100644
--- a/ppapi/proxy/plugin_resource_callback.h
+++ b/ppapi/proxy/plugin_resource_callback.h
@@ -33,7 +33,7 @@ class PluginResourceCallback : public PluginResourceCallbackBase {
   explicit PluginResourceCallback(const CallbackType& callback)
       : callback_(callback) {}
 
-  virtual void Run(
+  void Run(
       const ResourceMessageReplyParams& reply_params,
       const IPC::Message& msg) override {
     DispatchResourceReplyOrDefaultParams<MsgClass>(
@@ -41,7 +41,7 @@ class PluginResourceCallback : public PluginResourceCallbackBase {
   }
 
  private:
-  virtual ~PluginResourceCallback() {}
+  ~PluginResourceCallback() override {}
 
   CallbackType callback_;
 };