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

ppapi/proxy/plugin_resource_callback.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_PROXY_PLUGIN_RESOURCE_CALLBACK_H_
 #define PPAPI_PROXY_PLUGIN_RESOURCE_CALLBACK_H_
 
 #include "base/memory/ref_counted.h"
 #include "ipc/ipc_message.h"
 #include "ppapi/proxy/dispatch_reply_message.h"
@@ skipping 15 matching lines @@
   friend class base::RefCounted<PluginResourceCallbackBase>;
   virtual ~PluginResourceCallbackBase() {}
 };
 
 template<typename MsgClass, typename CallbackType>
 class PluginResourceCallback : public PluginResourceCallbackBase {
  public:
   explicit PluginResourceCallback(const CallbackType& callback)
       : callback_(callback) {}
 
-  virtual void Run(
+  void Run(
       const ResourceMessageReplyParams& reply_params,
       const IPC::Message& msg) override {
     DispatchResourceReplyOrDefaultParams<MsgClass>(
         &callback_, &CallbackType::Run, reply_params, msg);
   }
 
  private:
-  virtual ~PluginResourceCallback() {}
+  ~PluginResourceCallback() override {}
 
   CallbackType callback_;
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_PLUGIN_RESOURCE_CALLBACK_H_