Use css-device-adapt constraining for legacy viewport tags.

Source/core/css/resolver/ViewportStyleResolver.h

Index: Source/core/css/resolver/ViewportStyleResolver.h
diff --git a/Source/core/css/resolver/ViewportStyleResolver.h b/Source/core/css/resolver/ViewportStyleResolver.h
index 9f86309dd29b71b3959ff64999a537913982bddf..0f8116f560c5692193c80c2f18a75cc726c639c3 100644
--- a/Source/core/css/resolver/ViewportStyleResolver.h
+++ b/Source/core/css/resolver/ViewportStyleResolver.h
@@ -49,6 +49,7 @@ public:
 
     ~ViewportStyleResolver();
 
+    void setHasAuthorStyle() { m_hasAuthorStyle = true; }
     void addViewportRule(StyleRuleViewport*);
 
     void clearDocument();
@@ -61,6 +62,7 @@ private:
 
     Document* m_document;
     RefPtr<MutableStylePropertySet> m_propertySet;
+    bool m_hasAuthorStyle;
 };
 
 } // namespace WebCore