documentStyleSheetCollection() is always non-null.

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

Index: third_party/WebKit/Source/core/dom/StyleEngine.h
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.h b/third_party/WebKit/Source/core/dom/StyleEngine.h
index 409ec046e19a0cc45a3fb3f07598883d3a8cbf2b..9d4e6a4c96581dfe2a76e7e6506904acd264e1c8 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.h
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.h
@@ -254,12 +254,14 @@ class CORE_EXPORT StyleEngine final
                             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(