Provide default implementations for NotificationDelegate methods.

ui/message_center/notification_delegate.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 UI_MESSAGE_CENTER_NOTIFICATION_DELEGATE_H_
 #define UI_MESSAGE_CENTER_NOTIFICATION_DELEGATE_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "ui/message_center/message_center_export.h"
 
 namespace content {
 class RenderViewHost;
 }
 
 namespace message_center {
 
 // Delegate for a notification. This class has two roles: to implement callback
 // methods for notification, and to provide an identity of the associated
 // notification.
 class MESSAGE_CENTER_EXPORT NotificationDelegate
     : public base::RefCountedThreadSafe<NotificationDelegate> {
  public:
   // To be called when the desktop notification is actually shown.
-  virtual void Display() = 0;
+  virtual void Display();
 
   // To be called when the desktop notification cannot be shown due to an
   // error.
-  virtual void Error() = 0;
+  virtual void Error();
 
   // To be called when the desktop notification is closed.  If closed by a
   // user explicitly (as opposed to timeout/script), |by_user| should be true.
-  virtual void Close(bool by_user) = 0;
+  virtual void Close(bool by_user);
 
   // Returns true if the delegate can handle click event.
   virtual bool HasClickedListener();
 
   // To be called when a desktop notification is clicked.
-  virtual void Click() = 0;
+  virtual void Click();
 
-  // To be called when the user clicks a button in a notification. TODO(miket):
-  // consider providing default implementations of the pure virtuals of this
-  // interface, to avoid pinging so many OWNERs each time we enhance it.
+  // To be called when the user clicks a button in a notification.
   virtual void ButtonClick(int button_index);
 
  protected:
   virtual ~NotificationDelegate() {}
 
  private:
   friend class base::RefCountedThreadSafe<NotificationDelegate>;
 };
 
 // A simple notification delegate which invokes the passed closure when clicked.
 class MESSAGE_CENTER_EXPORT HandleNotificationClickedDelegate
     : public NotificationDelegate {
  public:
   explicit HandleNotificationClickedDelegate(const base::Closure& closure);
 
   // message_center::NotificationDelegate overrides:
-  void Display() override;
-  void Error() override;
-  void Close(bool by_user) override;
+  void Click() override;
   bool HasClickedListener() override;
-  void Click() override;
-  void ButtonClick(int button_index) override;
 
  protected:
   ~HandleNotificationClickedDelegate() override;
 
  private:
   std::string id_;
   base::Closure closure_;
 
   DISALLOW_COPY_AND_ASSIGN(HandleNotificationClickedDelegate);
 };
 
 // A notification delegate which invokes a callback when a notification button
 // has been clicked.
 class MESSAGE_CENTER_EXPORT HandleNotificationButtonClickDelegate
     : public NotificationDelegate {
  public:
   typedef base::Callback<void(int)> ButtonClickCallback;
 
   explicit HandleNotificationButtonClickDelegate(
       const ButtonClickCallback& button_callback);
 
   // message_center::NotificationDelegate overrides:
-  void Display() override;
-  void Error() override;
-  void Close(bool by_user) override;
-  void Click() override;
   void ButtonClick(int button_index) override;
 
  protected:
   ~HandleNotificationButtonClickDelegate() override;
 
  private:
   ButtonClickCallback button_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(HandleNotificationButtonClickDelegate);
 };
 
 }  //  namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_NOTIFICATION_DELEGATE_H_