Factor out uses of the WebContentsModalDialog interface from platform-independent code

chrome/browser/ui/webui/tab_modal_confirm_dialog_webui.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 CHROME_BROWSER_UI_WEBUI_TAB_MODAL_CONFIRM_DIALOG_WEBUI_H_
 #define CHROME_BROWSER_UI_WEBUI_TAB_MODAL_CONFIRM_DIALOG_WEBUI_H_
 
 #if !(defined(USE_AURA) || defined(OS_CHROMEOS))
 #error Tab-modal confirm dialog should be shown with native UI.
 #endif
@@ skipping 39 matching lines @@
     return constrained_web_dialog_delegate_;
   }
 
  private:
   virtual ~TabModalConfirmDialogWebUI();
 
   // TabModalConfirmDialog:
   virtual void AcceptTabModalDialog() OVERRIDE;
   virtual void CancelTabModalDialog() OVERRIDE;
 
+  // TabModalConfirmDialogCloseDelegate:
+  virtual void CloseDialog() OVERRIDE;
+
   scoped_ptr<TabModalConfirmDialogDelegate> delegate_;
 
   // Deletes itself.
   ConstrainedWebDialogDelegate* constrained_web_dialog_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(TabModalConfirmDialogWebUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_TAB_MODAL_CONFIRM_DIALOG_WEBUI_H_