Avoid stack allocating StyleSheetCollections.

third_party/WebKit/Source/core/dom/StyleSheetCollection.cpp

 /*
  * 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) 2013 Google Inc. All rights reserved.
  *
@@ skipping 16 matching lines @@
 #include "core/dom/StyleSheetCollection.h"
 
 #include "core/css/CSSStyleSheet.h"
 
 namespace blink {
 
 StyleSheetCollection::StyleSheetCollection()
 {
 }
 
+void StyleSheetCollection::dispose()
+{
+    m_styleSheetsForStyleSheetList.clear();
+    m_activeAuthorStyleSheets.clear();
+}
+
 void StyleSheetCollection::swap(StyleSheetCollection& other)
 {
     m_styleSheetsForStyleSheetList.swap(other.m_styleSheetsForStyleSheetList);
     m_activeAuthorStyleSheets.swap(other.m_activeAuthorStyleSheets);
 }
 
 void StyleSheetCollection::swapSheetsForSheetList(HeapVector<Member<StyleSheet>>& sheets)
 {
     // Only called for collection of HTML Imports that never has active sheets.
     DCHECK(m_activeAuthorStyleSheets.isEmpty());
@@ skipping 10 matching lines @@
     m_styleSheetsForStyleSheetList.append(sheet);
 }
 
 DEFINE_TRACE(StyleSheetCollection)
 {
     visitor->trace(m_activeAuthorStyleSheets);
     visitor->trace(m_styleSheetsForStyleSheetList);
 }
 
 } // namespace blink