Only allow one shadowRoot.

sky/engine/bindings/core/v8/V8GCController.cpp

 /*
  * Copyright (C) 2009 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 153 matching lines @@
             if (node->containsWrapper()) {
                 if (!node->isV8CollectableDuringMinorGC()) {
                     // This node is not in the new space of V8. This indicates that
                     // the minor GC cannot anyway judge reachability of this DOM tree.
                     // Thus we give up traversing the DOM tree.
                     return false;
                 }
                 node->clearV8CollectableDuringMinorGC();
                 partiallyDependentNodes->append(node);
             }
-            if (ShadowRoot* shadowRoot = node->youngestShadowRoot()) {
+            if (ShadowRoot* shadowRoot = node->shadowRoot()) {
                 if (!traverseTree(shadowRoot, partiallyDependentNodes))
                     return false;
-            } else if (node->isShadowRoot()) {
-                if (ShadowRoot* shadowRoot = toShadowRoot(node)->olderShadowRoot()) {
-                    if (!traverseTree(shadowRoot, partiallyDependentNodes))
-                        return false;
-                }
             }
             // <template> has a |content| property holding a DOM fragment which we must traverse,
             // just like we do for the shadow trees above.
             if (isHTMLTemplateElement(*node)) {
                 if (!traverseTree(toHTMLTemplateElement(*node).content(), partiallyDependentNodes))
                     return false;
             }
 
             // Document maintains the list of imported documents through HTMLImportsController.
             if (node->isDocumentNode()) {
@@ skipping 219 matching lines @@
     static size_t lastUsageReportedToV8 = 0;
 
     size_t currentUsage = Partitions::currentDOMMemoryUsage();
     int64_t diff = static_cast<int64_t>(currentUsage) - static_cast<int64_t>(lastUsageReportedToV8);
     isolate->AdjustAmountOfExternalAllocatedMemory(diff);
 
     lastUsageReportedToV8 = currentUsage;
 }
 
 } // namespace blink