Introduce positionForPoint() in LocalFrame class as replacement of visiblePositionForPoint()

Source/core/editing/DragCaretController.h

Index: Source/core/editing/DragCaretController.h
diff --git a/Source/core/editing/DragCaretController.h b/Source/core/editing/DragCaretController.h
index 19e6388e072b5ca7a5d56238c2c07191bb5cbe79..aa15965b6d3ce4f276a2bc378e255c2369f26557 100644
--- a/Source/core/editing/DragCaretController.h
+++ b/Source/core/editing/DragCaretController.h
@@ -44,8 +44,8 @@ public:
 
     bool hasCaret() const { return m_position.isNotNull(); }
     const VisiblePosition& caretPosition() { return m_position; }
-    void setCaretPosition(const VisiblePosition&);
-    void clear() { setCaretPosition(VisiblePosition()); }
+    void setCaretPosition(const PositionWithAffinity&);
+    void clear() { setCaretPosition(PositionWithAffinity()); }
 
     void nodeWillBeRemoved(Node&);