Make ElementShadow::oldestShadowRoot() return a reference

third_party/WebKit/Source/core/dom/shadow/ElementShadow.h

 /*
  * 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 27 matching lines @@
 namespace blink {
 
 class CORE_EXPORT ElementShadow final : public GarbageCollectedFinalized<ElementShadow> {
     WTF_MAKE_NONCOPYABLE(ElementShadow);
 public:
     static ElementShadow* create();
     ~ElementShadow();
 
     Element& host() const;
     ShadowRoot& youngestShadowRoot() const;
-    ShadowRoot* oldestShadowRoot() const { return m_shadowRoot; }
+    ShadowRoot& oldestShadowRoot() const { DCHECK(m_shadowRoot); return *m_shadowRoot; }
     ElementShadow* containingShadow() const;
 
     ShadowRoot& addShadowRoot(Element& shadowHost, ShadowRootType);
 
     bool hasSameStyles(const ElementShadow*) const;
 
     void attach(const Node::AttachContext&);
     void detach(const Node::AttachContext&);
 
     void willAffectSelector();
@@ skipping 70 matching lines @@
 inline void ElementShadow::distributeIfNeeded()
 {
     if (m_needsDistributionRecalc)
         distribute();
     m_needsDistributionRecalc = false;
 }
 
 } // namespace blink
 
 #endif