Make sure all paths out of the dialog properly unregister observers.

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h

 // Copyright 2016 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 CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_
 
 #include <memory>
 
 #include "base/callback_forward.h"
@@ skipping 49 matching lines @@
 
   // WebContentsObserver:
   void WasHidden() override;
 
   // BrowserListObserver:
   void OnBrowserSetLastActive(Browser* browser) override;
 
  private:
   friend class content::WebContentsUserData<JavaScriptDialogTabHelper>;
 
+  // Wrapper around a DialogClosedCallback so that we can intercept it before
+  // passing it onto the original callback.
+  void OnDialogClosed(DialogClosedCallback callback,
+                      bool success,
+                      const base::string16& user_input);
+
   void CloseDialog(bool suppress_callback,
                    bool success,
                    const base::string16& user_input);
 
+  void ClearDialogInfo();
+
   // The dialog being displayed on the observed WebContents.
   base::WeakPtr<JavaScriptDialog> dialog_;
 
   // The callback provided for when the dialog is closed. Usually the dialog
   // itself calls it, but in the cases where the dialog is closed not by the
   // user's input but by a call to |CloseDialog|, this class will call it.
   content::JavaScriptDialogManager::DialogClosedCallback dialog_callback_;
 
   base::Closure dialog_shown_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaScriptDialogTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_