Revert the feature of the <shadow> element as 'a function call' to the previous behavior.

Source/core/dom/shadow/InsertionPoint.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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 116 matching lines @@
 
 bool InsertionPoint::shouldUseFallbackElements() const
 {
     return isActive() && !hasDistribution();
 }
 
 bool InsertionPoint::canBeActive() const
 {
     if (!isInShadowTree())
         return false;
-    bool foundShadowElementInAncestors = false;
-    bool thisIsContentHTMLElement = hasTagName(contentTag);
     for (Node* node = parentNode(); node; node = node->parentNode()) {
-        if (node->isInsertionPoint()) {
-            // For HTMLContentElement, at most one HTMLShadowElement may appear in its ancestors.
-            if (thisIsContentHTMLElement && node->hasTagName(shadowTag) && !foundShadowElementInAncestors)
-                foundShadowElementInAncestors = true;
-            else
-                return false;
-        }
+        if (node->isInsertionPoint())
+            return false;
     }
     return true;
 }
 
 bool InsertionPoint::isActive() const
 {
     if (!canBeActive())
         return false;
     ShadowRoot* shadowRoot = containingShadowRoot();
     ASSERT(shadowRoot);
@@ skipping 150 matching lines @@
         if (!insertionPoints)
             return;
         for (size_t i = 0; i < insertionPoints->size(); ++i)
             results.append(insertionPoints->at(i).get());
         ASSERT(current != insertionPoints->last().get());
         current = insertionPoints->last().get();
     }
 }
 
 } // namespace WebCore