canMergeLists() should make sure that the list items do not belong to the same list

Source/core/editing/htmlediting.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 696 matching lines @@
         if (nextList == rootList)
             break;
         list = nextList;
     }
 
     return list;
 }
 
 bool canMergeLists(Element* firstList, Element* secondList)
 {
-    if (!firstList || !secondList || !firstList->isHTMLElement() || !secondList->isHTMLElement())
+    if (!firstList || !secondList || firstList == secondList || !firstList->isHTMLElement() || !secondList->isHTMLElement())

[yosin_UTC9, 2014/04/22 04:42:52]

I think caller should not pass same |Element| to |firstList| and |secondList|.
This case should be in assert rather than if-statement.

         return false;
 
     return firstList->hasTagName(secondList->tagQName()) // make sure the list types match (ol vs. ul)
     && firstList->rendererIsEditable() && secondList->rendererIsEditable() // both lists are editable
     && firstList->rootEditableElement() == secondList->rootEditableElement() // don't cross editing boundaries
     && isVisiblyAdjacent(positionInParentAfterNode(*firstList), positionInParentBeforeNode(*secondList));
     // Make sure there is no visible content between this li and the previous list
 }
 
 bool isRenderedTableElement(const Node* node)
@@ skipping 384 matching lines @@
     // if the selection starts just before a paragraph break, skip over it
     if (isEndOfParagraph(visiblePosition))
         return visiblePosition.next().deepEquivalent().downstream();
 
     // 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 visiblePosition.deepEquivalent().downstream();
 }
 
 } // namespace WebCore