documentStyleSheetCollection() is always non-null.

third_party/WebKit/Source/core/dom/StyleEngine.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 236 matching lines @@
   typedef HeapHashSet<Member<TreeScope>> UnorderedTreeScopeSet;
 
   void clearMediaQueryRuleSetOnTreeScopeStyleSheets(UnorderedTreeScopeSet&);
 
   void createResolver();
 
   CSSStyleSheet* parseSheet(Element&,
                             const String& text,
                             TextPosition startPosition);
 
-  const DocumentStyleSheetCollection* documentStyleSheetCollection() const {
-    return m_documentStyleSheetCollection.get();
+  const DocumentStyleSheetCollection& documentStyleSheetCollection() const {
+    DCHECK(m_documentStyleSheetCollection);
+    return *m_documentStyleSheetCollection;
   }
 
-  DocumentStyleSheetCollection* documentStyleSheetCollection() {
-    return m_documentStyleSheetCollection.get();
+  DocumentStyleSheetCollection& documentStyleSheetCollection() {
+    DCHECK(m_documentStyleSheetCollection);
+    return *m_documentStyleSheetCollection;
   }
 
   void updateActiveStyleSheetsInShadow(
       StyleResolverUpdateMode,
       TreeScope*,
       UnorderedTreeScopeSet& treeScopesRemoved);
 
   bool shouldSkipInvalidationFor(const Element&) const;
   void scheduleRuleSetInvalidationsForElement(
       Element&,
@@ skipping 46 matching lines @@
 
   std::unique_ptr<StyleResolverStats> m_styleResolverStats;
   unsigned m_styleForElementCount = 0;
 
   friend class StyleEngineTest;
 };
 
 }  // namespace blink
 
 #endif