Add DocumentMarkerList in preparation for DocumentMarkerController refactor

third_party/WebKit/Source/core/editing/markers/DocumentMarker.h

 /*
  * This file is part of the DOM implementation for WebCore.
  *
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * 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 153 matching lines @@
 
   struct MarkerOffsets {
     unsigned startOffset;
     unsigned endOffset;
   };
 
   Optional<MarkerOffsets> computeOffsetsAfterShift(unsigned offset,
                                                    unsigned oldLength,
                                                    unsigned newLength) const;
 
-  // Offset modifications are done by DocumentMarkerController.
-  // Other classes should not call following setters.
+  // Offset modifications are done by DocumentMarkerController and subclasses of
+  // DocumentMarkerList. Other classes should not call following setters.
   void setStartOffset(unsigned offset) { m_startOffset = offset; }
   void setEndOffset(unsigned offset) { m_endOffset = offset; }
   void shiftOffsets(int delta);
 
   DECLARE_TRACE();
 
  protected:
   DocumentMarker(const DocumentMarker&);
 
  private:
@@ skipping 17 matching lines @@
   virtual bool isDescription() const { return false; }
   virtual bool isTextMatch() const { return false; }
   virtual bool isComposition() const { return false; }
 
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 };
 
 }  // namespace blink
 
 #endif  // DocumentMarker_h