Avoid stack allocating StyleSheetCollections.

third_party/WebKit/Source/core/dom/StyleSheetCollection.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)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 26 matching lines @@
 
 class CSSStyleSheet;
 class StyleSheet;
 
 class CORE_EXPORT StyleSheetCollection : public GarbageCollected<StyleSheetCollection> {
     WTF_MAKE_NONCOPYABLE(StyleSheetCollection);
 public:
     friend class ActiveDocumentStyleSheetCollector;
     friend class ImportedDocumentStyleSheetCollector;
 
-    StyleSheetCollection();
+    static StyleSheetCollection* create()
+    {
+        return new StyleSheetCollection;
+    }
 
     const HeapVector<Member<CSSStyleSheet>>& activeAuthorStyleSheets() const { return m_activeAuthorStyleSheets; }
     const HeapVector<Member<StyleSheet>>& styleSheetsForStyleSheetList() const { return m_styleSheetsForStyleSheetList; }
 
     void swap(StyleSheetCollection&);
     void swapSheetsForSheetList(HeapVector<Member<StyleSheet>>&);
     void appendActiveStyleSheet(CSSStyleSheet*);
     void appendSheetForList(StyleSheet*);
 
     DECLARE_VIRTUAL_TRACE();
 
+    void dispose();
+
 protected:
+    StyleSheetCollection();
+
     HeapVector<Member<StyleSheet>> m_styleSheetsForStyleSheetList;
     HeapVector<Member<CSSStyleSheet>> m_activeAuthorStyleSheets;
 };
 
 } // namespace blink
 
 #endif // StyleSheetCollection_h