Templatize FrameSelection::contains function

Source/core/editing/VisibleSelection.h

Index: Source/core/editing/VisibleSelection.h
diff --git a/Source/core/editing/VisibleSelection.h b/Source/core/editing/VisibleSelection.h
index 841994993842d19206b320d1de0aea5643824051..f50f0a7e989479c3ef593bfa1c44186e0df2a568 100644
--- a/Source/core/editing/VisibleSelection.h
+++ b/Source/core/editing/VisibleSelection.h
@@ -54,6 +54,7 @@ public:
         static PositionType selectionEnd(const VisibleSelection& selection) { return selection.end(); }
         static VisiblePosition selectionVisibleStart(const VisibleSelection& selection) { return selection.visibleStart(); }
         static VisiblePosition selectionVisibleEnd(const VisibleSelection& selection) { return selection.visibleEnd(); }
+        static PositionType toPositionType(const Position& position) { return position; }
     };
 
     VisibleSelection();