ComposedTreeWalker does't have to return a node if an insertion point has no distributed nodes.

Source/core/dom/shadow/ComposedTreeWalker.cpp

 
 /*
  * Copyright (C) 2012 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 13 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/dom/shadow/ComposedTreeWalker.h"
 
 #include "core/dom/Element.h"
 #include "core/dom/shadow/ElementShadow.h"
 #include "core/dom/shadow/InsertionPoint.h"
+#include "core/html/shadow/HTMLContentElement.h"
 #include "core/html/shadow/HTMLShadowElement.h"
 
 namespace WebCore {
 
 static inline ElementShadow* shadowFor(const Node* node)
 {
     if (node && node->isElementNode())
         return toElement(node)->shadow();
     return 0;
 }
@@ skipping 22 matching lines @@
 }
 
 Node* ComposedTreeWalker::traverseNode(const Node* node, TraversalDirection direction)
 {
     ASSERT(node);
     if (!isActiveInsertionPoint(*node))
         return const_cast<Node*>(node);
     const InsertionPoint* insertionPoint = toInsertionPoint(node);
     if (Node* found = traverseDistributedNodes(direction == TraversalDirectionForward ? insertionPoint->first() : insertionPoint->last(), insertionPoint, direction))
         return found;
-    return traverseLightChildren(node, direction);
+    ASSERT(isHTMLShadowElement(node) || (isHTMLContentElement(node) && !node->hasChildNodes()));
+    return 0;
 }
 
 Node* ComposedTreeWalker::traverseDistributedNodes(const Node* node, const InsertionPoint* insertionPoint, TraversalDirection direction)
 {
     for (const Node* next = node; next; next = (direction == TraversalDirectionForward ? insertionPoint->nextTo(next) : insertionPoint->previousTo(next))) {
         if (Node* found = traverseNode(next, direction))
             return found;
     }
     return 0;
 }
@@ skipping 69 matching lines @@
     ShadowRoot* shadowRoot = toShadowRoot(parent);
     ASSERT(!shadowRoot->shadowInsertionPointOfYoungerShadowRoot());
     if (!shadowRoot->isYoungest())
         return 0;
     if (details)
         details->didTraverseShadowRoot(shadowRoot);
     return shadowRoot->host();
 }
 
 } // namespace