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

third_party/WebKit/Source/core/loader/EmptyClients.h

 /*
  * Copyright (C) 2006 Eric Seidel (eric@webkit.org)
  * Copyright (C) 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.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 93 matching lines @@
 
     void setMenubarVisible(bool) override {}
     bool menubarVisible() override { return false; }
 
     void setResizable(bool) override {}
 
     bool shouldReportDetailedMessageForSource(LocalFrame&, const String&) override { return false; }
     void addMessageToConsole(LocalFrame*, MessageSource, MessageLevel, const String&, unsigned, const String&, const String&) override {}
 
     bool canOpenBeforeUnloadConfirmPanel() override { return false; }
-    bool openBeforeUnloadConfirmPanelDelegate(LocalFrame*, const String&, bool) override { return true; }
+    bool openBeforeUnloadConfirmPanelDelegate(LocalFrame*, bool) override { return true; }
 
     void closeWindowSoon() override {}
 
     bool openJavaScriptAlertDelegate(LocalFrame*, const String&) override { return false; }
     bool openJavaScriptConfirmDelegate(LocalFrame*, const String&) override { return false; }
     bool openJavaScriptPromptDelegate(LocalFrame*, const String&, const String&, String&) override { return false; }
 
     bool hasOpenedPopup() const override { return false; }
     PassRefPtrWillBeRawPtr<PopupMenu> openPopupMenu(LocalFrame&, HTMLSelectElement&) override;
     DOMWindow* pagePopupWindowForTesting() const override { return nullptr; }
@@ skipping 210 matching lines @@
     ~EmptyDragClient() override {}
     DragDestinationAction actionMaskForDrag(DragData*) override { return DragDestinationActionNone; }
     void startDrag(DragImage*, const IntPoint&, const IntPoint&, DataTransfer*, LocalFrame*, bool) override {}
 };
 
 CORE_EXPORT void fillWithEmptyClients(Page::PageClients&);
 
 } // namespace blink
 
 #endif // EmptyClients_h