Move member function rootEditableElement() out from VisiblePosition class

Source/core/editing/EditingUtilities.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 285 matching lines @@
         node = node->parentNode();
 
     return node->rootEditableElement(editableType);
 }
 
 Element* editableRootForPosition(const PositionInComposedTree& p, EditableType editableType)
 {
     return editableRootForPosition(toPositionInDOMTree(p), editableType);
 }
 
+// TODO(yosin) This does not handle [table, 0] correctly.
+Element* rootEditableElementOf(const VisiblePosition& visiblePosition)
+{
+    Node* anchorNode = visiblePosition.deepEquivalent().anchorNode();
+    return anchorNode ? anchorNode->rootEditableElement() : nullptr;
+}
+
 // Finds the enclosing element until which the tree can be split.
 // When a user hits ENTER, he/she won't expect this element to be split into two.
 // You may pass it as the second argument of splitTreeToNode.
 Element* unsplittableElementForPosition(const Position& p)
 {
     // Since enclosingNodeOfType won't search beyond the highest root editable node,
     // this code works even if the closest table cell was outside of the root editable node.
     Element* enclosingCell = toElement(enclosingNodeOfType(p, &isTableCell));
     if (enclosingCell)
         return enclosingCell;
@@ skipping 1304 matching lines @@
     // if the selection starts just before a paragraph break, skip over it
     if (isEndOfParagraph(visiblePosition))
         return mostForwardCaretPosition(nextPositionOf(visiblePosition).deepEquivalent());
 
     // otherwise, make sure to be at the start of the first selected node,
     // instead of possibly at the end of the last node before the selection
     return mostForwardCaretPosition(visiblePosition.deepEquivalent());
 }
 
 } // namespace blink