Empty @viewport should not override legacy viewport.

Source/core/css/resolver/ViewportStyleResolver.cpp

 /*
  * Copyright (C) 2012-2013 Intel Corporation. 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 32 matching lines @@
     : m_document(document),
     m_hasAuthorStyle(false)
 {
     ASSERT(m_document);
 }
 
 ViewportStyleResolver::~ViewportStyleResolver()
 {
 }
 
-void ViewportStyleResolver::addViewportRule(StyleRuleViewport* viewportRule)
+void ViewportStyleResolver::collectViewportRules(RuleSet* rules, Origin origin)
+{
+    rules->compactRulesIfNeeded();
+
+    const Vector<StyleRuleViewport*>& viewportRules = rules->viewportRules();
+    for (size_t i = 0; i < viewportRules.size(); ++i)
+        addViewportRule(viewportRules[i], origin);
+}
+
+void ViewportStyleResolver::addViewportRule(StyleRuleViewport* viewportRule, Origin origin)
 {
     StylePropertySet* propertySet = viewportRule->mutableProperties();
 
     unsigned propertyCount = propertySet->propertyCount();
     if (!propertyCount)
         return;
 
+    if (origin == AuthorOrigin)
+        m_hasAuthorStyle = true;
+
     if (!m_propertySet) {
         m_propertySet = propertySet->mutableCopy();
         return;
     }
 
     // We cannot use mergeAndOverrideOnConflict() here because it doesn't
     // respect the !important declaration (but addParsedProperty() does).
     for (unsigned i = 0; i < propertyCount; ++i)
         m_propertySet->addParsedProperty(propertySet->propertyAt(i).toCSSProperty());
 }
@@ skipping 114 matching lines @@
     case CSSValueAuto:
         return Length();
     default:
         // Unrecognized keyword.
         ASSERT_NOT_REACHED();
         return Length(0, Fixed);
     }
 }
 
 } // namespace WebCore