Observe in views::InputMethodBridge if host IME is destroyed

ui/views/ime/input_method_bridge.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 UI_VIEWS_IME_INPUT_METHOD_BRIDGE_H_
 #define UI_VIEWS_IME_INPUT_METHOD_BRIDGE_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 66 matching lines @@
   virtual void ExtendSelectionAndDelete(size_t before, size_t after) OVERRIDE;
   virtual void EnsureCaretInRect(const gfx::Rect& rect) OVERRIDE;
 
   // Overridden from FocusChangeListener.
   virtual void OnWillChangeFocus(View* focused_before, View* focused) OVERRIDE;
   virtual void OnDidChangeFocus(View* focused_before, View* focused) OVERRIDE;
 
   ui::InputMethod* GetHostInputMethod() const;
 
  private:
+  class HostObserver;
+
   void UpdateViewFocusState();
 
-  ui::InputMethod* const host_;
+  ui::InputMethod* host_;
+
+  // An observer observing the host input method for cases that the host input
+  // method is destroyed before this bridge input method.
+  scoped_ptr<HostObserver> host_observer_;
 
   const bool shared_input_method_;
 
   DISALLOW_COPY_AND_ASSIGN(InputMethodBridge);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_IME_INPUT_METHOD_BRIDGE_H_