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

ppapi/proxy/network_proxy_resource.h

 // Copyright (c) 2013 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_NETWORK_PROXY_RESOURCE_H_
 #define PPAPI_PROXY_NETWORK_PROXY_RESOURCE_H_
 
 #include "ppapi/proxy/plugin_resource.h"
 #include "ppapi/proxy/ppapi_proxy_export.h"
 #include "ppapi/thunk/ppb_network_proxy_api.h"
 
 namespace ppapi {
 namespace proxy {
 
 // The proxy-side resource for PPB_NetworkProxy.
 class PPAPI_PROXY_EXPORT NetworkProxyResource
       : public PluginResource,
         public thunk::PPB_NetworkProxy_API {
  public:
   NetworkProxyResource(Connection connection, PP_Instance instance);
-  virtual ~NetworkProxyResource();
+  ~NetworkProxyResource() override;
 
  private:
   // Resource implementation.
-  virtual thunk::PPB_NetworkProxy_API* AsPPB_NetworkProxy_API() override;
+  thunk::PPB_NetworkProxy_API* AsPPB_NetworkProxy_API() override;
 
   // PPB_NetworkProxy_API implementation.
-  virtual int32_t GetProxyForURL(
+  int32_t GetProxyForURL(
       PP_Instance instance,
       PP_Var url,
       PP_Var* proxy_string,
       scoped_refptr<TrackedCallback> callback) override;
 
   void OnPluginMsgGetProxyForURLReply(PP_Var* proxy_string_out_param,
                                       scoped_refptr<TrackedCallback> callback,
                                       const ResourceMessageReplyParams& params,
                                       const std::string& proxy_string);
 
   DISALLOW_COPY_AND_ASSIGN(NetworkProxyResource);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_NETWORK_PROXY_RESOURCE_H_