Make ElementShadow::oldestShadowRoot() return a reference

third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 403 matching lines @@
         return nullptr;
     return treeScope->scopedStyleResolver();
 }
 
 static void matchHostRules(const Element& element, ElementRuleCollector& collector)
 {
     ElementShadow* shadow = element.shadow();
     if (!shadow)
         return;
 
-    for (ShadowRoot* shadowRoot = shadow->oldestShadowRoot(); shadowRoot; shadowRoot = shadowRoot->youngerShadowRoot()) {
+    for (ShadowRoot* shadowRoot = &shadow->oldestShadowRoot(); shadowRoot; shadowRoot = shadowRoot->youngerShadowRoot()) {
         if (!shadowRoot->numberOfStyles())
             continue;
         if (ScopedStyleResolver* resolver = shadowRoot->scopedStyleResolver()) {
             collector.clearMatchedRules();
             resolver->collectMatchingShadowHostRules(collector);
             collector.sortAndTransferMatchedRules();
             collector.finishAddingAuthorRulesForTreeScope();
         }
     }
 }
@@ skipping 1309 matching lines @@
     visitor->trace(m_siblingRuleSet);
     visitor->trace(m_uncommonAttributeRuleSet);
     visitor->trace(m_watchedSelectorsRules);
     visitor->trace(m_treeBoundaryCrossingScopes);
     visitor->trace(m_styleSharingLists);
     visitor->trace(m_pendingStyleSheets);
     visitor->trace(m_document);
 }
 
 } // namespace blink