(Chrome OS) Notify when the candidate window is opened/closed.

chrome/browser/chromeos/input_method/candidate_window.h

 // Copyright (c) 2011 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.
 //
 // This file implements the input method candidate window used on Chrome OS.
 
 #ifndef CHROME_BROWSER_CHROMEOS_INPUT_METHOD_CANDIDATE_WINDOW_H_
 #define CHROME_BROWSER_CHROMEOS_INPUT_METHOD_CANDIDATE_WINDOW_H_
 #pragma once
 
 #include "base/basictypes.h"
 
 namespace chromeos {
 namespace input_method {
 
 // CandidateWindowController is used for controlling the input method
 // candidate window. Once the initialization is done, the controller
 // starts monitoring signals sent from the the background input method
 // daemon, and shows and hides the candidate window as neeeded. Upon
 // deletion of the object, monitoring stops and the view used for
 // rendering the candidate view is deleted.
 class CandidateWindowController {
  public:
+  class Observer {
+   public:
+    virtual ~Observer() {}
+
+    virtual void CandidateWindowOpened() = 0;
+    virtual void CandidateWindowClosed() = 0;
+  };
+
   CandidateWindowController();
   virtual ~CandidateWindowController();
 
   // Initializes the candidate window. Returns true on success.
   bool Init();
 
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
  private:
   class Impl;
   Impl* impl_;
   DISALLOW_COPY_AND_ASSIGN(CandidateWindowController);
 };
 
 }  // namespace input_method
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_INPUT_METHOD_CANDIDATE_WINDOW_H_