Makes sure that an input method doesn't reference to a destroyed object.

ui/base/ime/input_method_base.cc

 // 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.
 
 #include "ui/base/ime/input_method_base.h"
 
 #include "base/logging.h"
 #include "ui/base/ime/input_method_delegate.h"
 #include "ui/base/ime/input_method_observer.h"
 #include "ui/base/ime/text_input_client.h"
@@ skipping 34 matching lines @@
 void InputMethodBase::SetFocusedTextInputClient(TextInputClient* client) {
   TextInputClient* old = text_input_client_;
   OnWillChangeFocusedClient(old, client);
   text_input_client_ = client;  // NULL allowed.
   OnDidChangeFocusedClient(old, client);
 
   if (old != text_input_client_)
     NotifyTextInputStateChanged(text_input_client_);
 }
 
+void InputMethodBase::DetachTextInputClient(TextInputClient* client) {
+  if (text_input_client_ == client) {
+    OnWillChangeFocusedClient(client, NULL);
+    text_input_client_ = NULL;
+    OnDidChangeFocusedClient(client, NULL);
+    NotifyTextInputStateChanged(text_input_client_);
+  }
+}
+
 TextInputClient* InputMethodBase::GetTextInputClient() const {
   return system_toplevel_window_focused_ ? text_input_client_ : NULL;
 }
 
 void InputMethodBase::OnTextInputTypeChanged(const TextInputClient* client) {
   if (!IsTextInputClientFocused(client))
     return;
   NotifyTextInputStateChanged(client);
 }
 
@@ skipping 47 matching lines @@
 }
 
 void InputMethodBase::NotifyTextInputStateChanged(
     const TextInputClient* client) {
   FOR_EACH_OBSERVER(InputMethodObserver,
                     observer_list_,
                     OnTextInputStateChanged(client));
 }
 
 }  // namespace ui