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 b9bf08bdfb148e152f73b14bc32e7ee9ca762dcc..551349417232e8c6cf91fcbae395533c28ef5074 100644
--- a/Source/core/css/resolver/ViewportStyleResolver.h
+++ b/Source/core/css/resolver/ViewportStyleResolver.h
@@ -50,6 +50,7 @@ public:
 
     ~ViewportStyleResolver();
 
+    void setHasAuthorStyle() { m_hasAuthorStyle = true; }
     void addViewportRule(StyleRuleViewport*);
 
     void clearDocument();
@@ -63,6 +64,7 @@ private:
 
     Document* m_document;
     RefPtr<MutableStylePropertySet> m_propertySet;
+    bool m_hasAuthorStyle;
 };
 
 } // namespace WebCore