Allow <link rel=stylesheet> in a connected shadow tree

third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 209 matching lines @@
 }
 
 void StyleResolver::removePendingAuthorStyleSheets(const HeapVector<Member<CSSStyleSheet>>& styleSheets)
 {
     for (unsigned i = 0; i < styleSheets.size(); ++i)
         m_pendingStyleSheets.remove(styleSheets[i].get());
 }
 
 void StyleResolver::appendCSSStyleSheet(CSSStyleSheet& cssSheet)
 {
-    ASSERT(!cssSheet.disabled());
-    ASSERT(cssSheet.ownerDocument());
-    ASSERT(cssSheet.ownerNode());
-    ASSERT(isHTMLStyleElement(cssSheet.ownerNode()) || isSVGStyleElement(cssSheet.ownerNode()) || cssSheet.ownerNode()->treeScope() == cssSheet.ownerDocument());
+    DCHECK(!cssSheet.disabled());
+    DCHECK(cssSheet.ownerDocument());
+    DCHECK(cssSheet.ownerNode());
+    DCHECK(isHTMLStyleElement(cssSheet.ownerNode()) || isSVGStyleElement(cssSheet.ownerNode()) || cssSheet.ownerNode()->isConnected());
 
     if (cssSheet.mediaQueries() && !m_medium->eval(cssSheet.mediaQueries(), &m_viewportDependentMediaQueryResults, &m_deviceDependentMediaQueryResults))
         return;
 
     TreeScope* treeScope = &cssSheet.ownerNode()->treeScope();
     // TODO(rune@opera.com): This is a workaround for crbug.com/559292
     // when we're in the middle of removing a subtree with a style element
     // and the treescope has been changed but inDocument and isInShadowTree
     // are not.
     //
@@ skipping 1499 matching lines @@
     visitor->trace(m_siblingRuleSet);
     visitor->trace(m_uncommonAttributeRuleSet);
     visitor->trace(m_watchedSelectorsRules);
     visitor->trace(m_treeBoundaryCrossingScopes);
     visitor->trace(m_styleSharingLists);
     visitor->trace(m_pendingStyleSheets);
     visitor->trace(m_document);
 }
 
 } // namespace blink