Remove the ability of webpages to specify strings for the onbeforeunload dialog.

content/renderer/render_frame_impl.h

 // Copyright 2013 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 CONTENT_RENDERER_RENDER_FRAME_IMPL_H_
 #define CONTENT_RENDERER_RENDER_FRAME_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 504 matching lines @@
   void didChangeSelection(bool is_empty_selection) override;
   blink::WebColorChooser* createColorChooser(
       blink::WebColorChooserClient* client,
       const blink::WebColor& initial_color,
       const blink::WebVector<blink::WebColorSuggestion>& suggestions) override;
   void runModalAlertDialog(const blink::WebString& message) override;
   bool runModalConfirmDialog(const blink::WebString& message) override;
   bool runModalPromptDialog(const blink::WebString& message,
                             const blink::WebString& default_value,
                             blink::WebString* actual_value) override;
-  bool runModalBeforeUnloadDialog(bool is_reload,
-                                  const blink::WebString& message) override;
+  bool runModalBeforeUnloadDialog(bool is_reload) override;
   void showContextMenu(const blink::WebContextMenuData& data) override;
   void clearContextMenu() override;
   void willSendRequest(blink::WebLocalFrame* frame,
                        unsigned identifier,
                        blink::WebURLRequest& request,
                        const blink::WebURLResponse& redirect_response) override;
   void didReceiveResponse(unsigned identifier,
                           const blink::WebURLResponse& response) override;
   void didLoadResourceFromMemoryCache(
       const blink::WebURLRequest& request,
@@ skipping 671 matching lines @@
 #endif
 
   base::WeakPtrFactory<RenderFrameImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderFrameImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_FRAME_IMPL_H_