Fix the issue introduced by hooking window.onbeforeunload in WebDialogView which breaks WebDialogUI…

ui/web_dialogs/web_dialog_delegate.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_WEB_DIALOGS_WEB_DIALOG_DELEGATE_H_
 #define UI_WEB_DIALOGS_WEB_DIALOG_DELEGATE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 61 matching lines @@
   // |render_view_host| is the RenderViewHost for the shown dialog.
   virtual void OnDialogShown(content::WebUI* webui,
                              content::RenderViewHost* render_view_host) {}
 
   // A callback to notify the delegate that the dialog closed.
   // IMPORTANT: Implementations should delete |this| here (unless they've
   // arranged for the delegate to be deleted in some other way, e.g. by
   // registering it as a message handler in the WebUI object).
   virtual void OnDialogClosed(const std::string& json_retval) = 0;
 
+  // A callback to notify the delegate that the dialog is being closed in
+  // response to a "DialogClose" message from WebUI.
+  virtual void OnDialogCloseFromWebUI(const std::string& json_retval);
+
   // A callback to notify the delegate that the contents have gone
   // away. Only relevant if your dialog hosts code that calls
   // windows.close() and you've allowed that.  If the output parameter
   // is set to true, then the dialog is closed.  The default is false.
   virtual void OnCloseContents(content::WebContents* source,
                                bool* out_close_dialog) = 0;
 
   // A callback to allow the delegate to dictate that the window should not
   // have a title bar.  This is useful when presenting branded interfaces.
   virtual bool ShouldShowDialogTitle() const = 0;
@@ skipping 24 matching lines @@
 
   // Stores the dialog bounds.
   virtual void StoreDialogSize(const gfx::Size& dialog_size) {}
 
   virtual ~WebDialogDelegate() {}
 };
 
 }  // namespace ui
 
 #endif  // UI_WEB_DIALOGS_WEB_DIALOG_DELEGATE_H_