Use Position instead of VisiblePosition for SurroundingText.

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 571a2d5aa189cc9ed7983dd85f0b6b5b446847d5..d3e04ee9eacc206c0e0d13b26284ea647e7045a2 100644
--- a/Source/core/editing/SurroundingText.h
+++ b/Source/core/editing/SurroundingText.h
@@ -36,13 +36,13 @@
 
 namespace WebCore {
 
+class Position;
 class Range;
-class VisiblePosition;
 
 class SurroundingText {
     WTF_MAKE_NONCOPYABLE(SurroundingText);
 public:
-    SurroundingText(const VisiblePosition&, unsigned maxLength);
+    SurroundingText(const Position&, unsigned maxLength);
 
     String content() const;
     unsigned positionOffsetInContent() const;