Remove unused/unneeded code from core/editing.

Source/core/editing/TextCheckingHelper.h

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 41 matching lines @@
     String textSubstring(unsigned pos, unsigned len = INT_MAX) const { return text().substring(pos, len); }
     UChar textCharAt(int index) const { return text()[static_cast<unsigned>(index)]; }
 
     bool isEmpty() const;
     bool isTextEmpty() const { return text().isEmpty(); }
     bool isRangeEmpty() const { return checkingStart() >= checkingEnd(); }
 
     int checkingStart() const;
     int checkingEnd() const;
     int checkingLength() const;
-    String checkingSubstring() const { return textSubstring(checkingStart(), checkingLength()); }
 
     bool checkingRangeCovers(int location, int length) const { return location < checkingEnd() && location + length > checkingStart(); }
     PassRefPtrWillBeRawPtr<Range> paragraphRange() const;
     PassRefPtrWillBeRawPtr<Range> checkingRange() const { return m_checkingRange; }
 
 private:
     void invalidateParagraphRangeValues();
     PassRefPtrWillBeRawPtr<Range> offsetAsRange() const;
 
     RefPtrWillBeMember<Range> m_checkingRange;
@@ skipping 27 matching lines @@
     bool unifiedTextCheckerEnabled() const;
 };
 
 void checkTextOfParagraph(TextCheckerClient&, const String&, TextCheckingTypeMask, Vector<TextCheckingResult>&);
 
 bool unifiedTextCheckerEnabled(const LocalFrame*);
 
 } // namespace blink
 
 #endif // TextCheckingHelper_h