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

third_party/WebKit/Source/core/page/ChromeClient.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple, Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 251 matching lines @@
     // that this is comprehensive.
     virtual void didObserveNonGetFetchFromScript() const {}
 
     virtual PassOwnPtr<WebFrameScheduler> createFrameScheduler() = 0;
 
 protected:
     ~ChromeClient() override { }
 
     virtual void showMouseOverURL(const HitTestResult&) = 0;
     virtual void setWindowRect(const IntRect&) = 0;
-    virtual bool openBeforeUnloadConfirmPanelDelegate(LocalFrame*, const String& message, bool isReload) = 0;
+    virtual bool openBeforeUnloadConfirmPanelDelegate(LocalFrame*, bool isReload) = 0;
     virtual bool openJavaScriptAlertDelegate(LocalFrame*, const String&) = 0;
     virtual bool openJavaScriptConfirmDelegate(LocalFrame*, const String&) = 0;
     virtual bool openJavaScriptPromptDelegate(LocalFrame*, const String& message, const String& defaultValue, String& result) = 0;
     virtual void printDelegate(LocalFrame*) = 0;
 
 private:
     bool canOpenModalIfDuringPageDismissal(Frame* mainFrame, DialogType, const String& message);
     void setToolTip(const HitTestResult&);
 
     LayoutPoint m_lastToolTipPoint;
     String m_lastToolTipText;
 
     FRIEND_TEST_ALL_PREFIXES(ChromeClientTest, SetToolTipFlood);
 };
 
 } // namespace blink
 
 #endif // ChromeClient_h