Remove the unused LocalFrame::documentTypeString() function

Source/core/frame/LocalFrame.h

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999-2001 Lars Knoll <knoll@kde.org>
  *                     1999-2001 Antti Koivisto <koivisto@kde.org>
  *                     2000-2001 Simon Hausmann <hausmann@kde.org>
  *                     2000-2001 Dirk Mueller <mueller@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
@@ skipping 126 matching lines @@
 
         void setPageZoomFactor(float factor);
         float pageZoomFactor() const { return m_pageZoomFactor; }
         void setTextZoomFactor(float factor);
         float textZoomFactor() const { return m_textZoomFactor; }
         void setPageAndTextZoomFactors(float pageZoomFactor, float textZoomFactor);
 
         void deviceOrPageScaleFactorChanged();
         double devicePixelRatio() const;
 
-        String documentTypeString() const;
-
         PassOwnPtr<DragImage> nodeImage(Node&);
         PassOwnPtr<DragImage> dragImageForSelection();
 
         String selectedText() const;
         String selectedTextForClipboard() const;
 
         VisiblePosition visiblePositionForPoint(const IntPoint& framePoint);
         Document* documentAtPoint(const IntPoint& windowPoint);
         PassRefPtrWillBeRawPtr<Range> rangeForPoint(const IntPoint& framePoint);
 
@@ skipping 130 matching lines @@
     DEFINE_TYPE_CASTS(LocalFrame, Frame, localFrame, localFrame->isLocalFrame(), localFrame.isLocalFrame());
 
 } // namespace blink
 
 // During refactoring, there are some places where we need to do type conversions that
 // will not be needed once all instances of LocalFrame and RemoteFrame are sorted out.
 // At that time this #define will be removed and all the uses of it will need to be corrected.
 #define toLocalFrameTemporary toLocalFrame
 
 #endif // LocalFrame_h