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

cloud_print/gcp20/prototype/cloud_print_xmpp_listener.h

 // Copyright 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 CLOUD_PRINT_GCP20_PROTOTYPE_CLOUD_PRINT_XMPP_LISTENER_H_
 #define CLOUD_PRINT_GCP20_PROTOTYPE_CLOUD_PRINT_XMPP_LISTENER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 47 matching lines @@
     // Invoked when printer was deleted from the server.
     virtual void OnXmppDeleteNotification(const std::string& device_id) = 0;
   };
 
   CloudPrintXmppListener(
       const std::string& robot_email,
       int standard_ping_interval,
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
       Delegate* delegate);
 
-  virtual ~CloudPrintXmppListener();
+  ~CloudPrintXmppListener() override;
 
   // Connects to the server.
   void Connect(const std::string& access_token);
 
   // Update ping interval when new local_settings was received.
   void set_ping_interval(int interval);
 
  private:
   // notifier::PushClientObserver methods:
-  virtual void OnNotificationsEnabled() override;
-  virtual void OnNotificationsDisabled(
+  void OnNotificationsEnabled() override;
+  void OnNotificationsDisabled(
       notifier::NotificationsDisabledReason reason) override;
-  virtual void OnIncomingNotification(
+  void OnIncomingNotification(
       const notifier::Notification& notification) override;
-  virtual void OnPingResponse() override;
+  void OnPingResponse() override;
 
   // Stops listening and sending pings.
   void Disconnect();
 
   // Schedules ping (unless it was already scheduled).
   void SchedulePing();
 
   // Sends ping.
   void SendPing();
 
@@ skipping 23 matching lines @@
 
   scoped_refptr<net::URLRequestContextGetter> context_getter_;
 
   Delegate* delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(CloudPrintXmppListener);
 };
 
 #endif  // CLOUD_PRINT_GCP20_PROTOTYPE_CLOUD_PRINT_XMPP_LISTENER_H_