Remove the unused LocalFrame::documentTypeString() function

Source/core/frame/LocalFrame.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Simon Hausmann <hausmann@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  *                     2001 George Staikos <staikos@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov <ap@nypop.com>
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 552 matching lines @@
 double LocalFrame::devicePixelRatio() const
 {
     if (!m_host)
         return 0;
 
     double ratio = m_host->deviceScaleFactor();
     ratio *= pageZoomFactor();
     return ratio;
 }
 
-String LocalFrame::documentTypeString() const
-{
-    if (DocumentType* doctype = document()->doctype())
-        return createMarkup(doctype);
-
-    return String();
-}
-
 PassOwnPtr<DragImage> LocalFrame::nodeImage(Node& node)
 {
     if (!node.renderer())
         return nullptr;
 
     const ScopedFramePaintingState state(this, &node);
 
     m_view->updateLayoutAndStyleForPainting();
 
     m_view->setPaintBehavior(state.paintBehavior | PaintBehaviorFlattenCompositingLayers);
@@ skipping 202 matching lines @@
     // We detach the FrameView's custom scroll bars as early as
     // possible to prevent m_doc->detach() from messing with the view
     // such that its scroll bars won't be torn down.
     //
     // FIXME: We should revisit this.
     if (m_view)
         m_view->prepareForDetach();
 }
 
 } // namespace blink