Make SurroundingText work for a Range.

Source/core/editing/SurroundingText.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 24 matching lines @@
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
 class Position;
 class Range;
 
 class SurroundingText {
     WTF_MAKE_NONCOPYABLE(SurroundingText);
 public:
+    SurroundingText(const Range&, unsigned maxLength);
     SurroundingText(const Position&, unsigned maxLength);
 
     String content() const;
-    unsigned positionOffsetInContent() const;
+    unsigned startOffsetInContent() const;
+    unsigned endOffsetInContent() const;
 
     PassRefPtrWillBeRawPtr<Range> rangeFromContentOffsets(unsigned startOffsetInContent, unsigned endOffsetInContent);
 
 private:
+    void initialize(const Position&, const Position&, unsigned maxLength);
+
     RefPtrWillBePersistent<Range> m_contentRange;
-    size_t m_positionOffsetInContent;
+    size_t m_startOffsetInContent;
+    size_t m_endOffsetInContent;
 };
 
 } // namespace WebCore
 
 #endif // SurroundingText_h