Empty @viewport should not override legacy viewport.

Source/core/css/resolver/ViewportStyleResolver.cpp

Index: Source/core/css/resolver/ViewportStyleResolver.cpp
diff --git a/Source/core/css/resolver/ViewportStyleResolver.cpp b/Source/core/css/resolver/ViewportStyleResolver.cpp
index f38f7d78060e3820d8a3cfbfe6a31d572e1e7795..3d701961422c264a127efda12a6bb062d97bbd17 100644
--- a/Source/core/css/resolver/ViewportStyleResolver.cpp
+++ b/Source/core/css/resolver/ViewportStyleResolver.cpp
@@ -50,7 +50,16 @@ 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();
 
@@ -58,6 +67,9 @@ void ViewportStyleResolver::addViewportRule(StyleRuleViewport* viewportRule)
     if (!propertyCount)
         return;
 
+    if (origin == AuthorOrigin)
+        m_hasAuthorStyle = true;
+
     if (!m_propertySet) {
         m_propertySet = propertySet->mutableCopy();
         return;