Make SurroundingText work for a Range.

Source/core/editing/SurroundingText.h

Index: Source/core/editing/SurroundingText.h
diff --git a/Source/core/editing/SurroundingText.h b/Source/core/editing/SurroundingText.h
index d3e04ee9eacc206c0e0d13b26284ea647e7045a2..28b885e0c6d9f75603aa44c480dff4b5c7c4c1f7 100644
--- a/Source/core/editing/SurroundingText.h
+++ b/Source/core/editing/SurroundingText.h
@@ -42,16 +42,21 @@ 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 process(const Position&, const Position&, unsigned maxLength);
+
     RefPtrWillBePersistent<Range> m_contentRange;
-    size_t m_positionOffsetInContent;
+    size_t m_startOffsetInContent;
+    size_t m_endOffsetInContent;
 };
 
 } // namespace WebCore