Don't generate RuleSets for viewport UA sheets.

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/)
@@ skipping 164 matching lines @@
        shadowRoot = shadowRoot->olderShadowRoot()) {
     if (shadowRoot->numberOfStyles() > 0) {
       if (ScopedStyleResolver* resolver = shadowRoot->scopedStyleResolver())
         resolvers.append(resolver);
     }
   }
 }
 
 StyleResolver::StyleResolver(Document& document)
     : m_document(document),
-      m_viewportStyleResolver(ViewportStyleResolver::create(&document)),
+      m_viewportStyleResolver(ViewportStyleResolver::create(document)),
       m_needCollectFeatures(false),
       m_printMediaType(false),
       m_styleSharingDepth(0) {
   FrameView* view = document.view();
   if (view) {
     m_medium = new MediaQueryEvaluator(&view->frame());
     m_printMediaType =
         equalIgnoringCase(view->mediaType(), MediaTypeNames::print);
   } else {
     m_medium = new MediaQueryEvaluator("all");
@@ skipping 1753 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