Empty @viewport should not override legacy viewport.

Source/core/css/resolver/ScopedStyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 16 matching lines @@
 #include "config.h"
 #include "core/css/resolver/ScopedStyleResolver.h"
 
 #include "HTMLNames.h"
 #include "core/css/CSSStyleSheet.h"
 #include "core/css/PageRuleCollector.h"
 #include "core/css/RuleFeature.h"
 #include "core/css/RuleSet.h"
 #include "core/css/StyleRule.h"
 #include "core/css/resolver/StyleResolver.h" // For MatchRequest.
+#include "core/css/resolver/ViewportStyleResolver.h"
 #include "core/dom/Document.h"
 #include "core/dom/shadow/ElementShadow.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/html/HTMLStyleElement.h"
 
 namespace WebCore {
 
 ScopedStyleResolver* ScopedStyleTree::ensureScopedStyleResolver(const ContainerNode& scopingNode)
 {
     bool isNewEntry;
@@ skipping 373 matching lines @@
 
 void ScopedStyleResolver::matchPageRules(PageRuleCollector& collector)
 {
     // Only consider the global author RuleSet for @page rules, as per the HTML5 spec.
     ASSERT(m_scopingNode.isDocumentNode());
     collector.matchPageRules(m_authorStyle.get());
 }
 
 void ScopedStyleResolver::collectViewportRulesTo(StyleResolver* resolver) const
 {
+    // Only consider the global author RuleSet for @viewport rules.
+    ASSERT(m_scopingNode.isDocumentNode());
     if (m_authorStyle)
-        resolver->collectViewportRules(m_authorStyle.get(), StyleResolver::AuthorOrigin);
+        resolver->viewportStyleResolver()->collectViewportRules(m_authorStyle.get(), ViewportStyleResolver::AuthorOrigin);
 }
 
 } // namespace WebCore