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

third_party/WebKit/public/web/WebFrameClient.h

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 382 matching lines @@
 
     // Displays a modal input dialog with the given message as description
     // and OK/Cancel choices. The input field is pre-filled with
     // defaultValue. Returns true if the user selects 'OK' or false
     // otherwise. Upon returning true, actualValue contains the value of
     // the input field.
     virtual bool runModalPromptDialog(
         const WebString& message, const WebString& defaultValue,
         WebString* actualValue) { return false; }
 
-    // Displays a modal confirmation dialog containing the given message as
-    // description and OK/Cancel choices, where 'OK' means that it is okay
-    // to proceed with closing the view. Returns true if the user selects
-    // 'OK' or false otherwise.
-    virtual bool runModalBeforeUnloadDialog(
-        bool isReload, const WebString& message) { return true; }
+    // Displays a modal confirmation dialog with OK/Cancel choices, where 'OK'
+    // means that it is okay to proceed with closing the view. Returns true if
+    // the user selects 'OK' or false otherwise.
+    virtual bool runModalBeforeUnloadDialog(bool isReload) { return true; }
 
 
     // UI ------------------------------------------------------------------
 
     // Shows a context menu with commands relevant to a specific element on
     // the given frame. Additional context data is supplied.
     virtual void showContextMenu(const WebContextMenuData&) { }
 
     // Called when the data attached to the currently displayed context menu is
     // invalidated. The context menu may be closed if possible.
@@ skipping 285 matching lines @@
     // This method takes ownership of the callbacks pointer.
     virtual void checkIfAudioSinkExistsAndIsAuthorized(const WebString& sinkId, const WebSecurityOrigin&, WebSetSinkIdCallbacks*) { BLINK_ASSERT_NOT_REACHED(); }
 
 protected:
     virtual ~WebFrameClient() { }
 };
 
 } // namespace blink
 
 #endif