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

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 34239374452d71ee590cdda4ac0ae685e9848c03..9ef92be215bbb201784cb9d9f55e194741e07dc4 100644
--- a/Source/core/css/resolver/ViewportStyleResolver.cpp
+++ b/Source/core/css/resolver/ViewportStyleResolver.cpp
@@ -40,7 +40,8 @@
 namespace WebCore {
 
 ViewportStyleResolver::ViewportStyleResolver(Document* document)
-    : m_document(document)
+    : m_document(document),
+    m_hasAuthorStyle(false)
 {
     ASSERT(m_document);
 }
@@ -78,19 +79,17 @@ void ViewportStyleResolver::resolve()
     if (!m_document)
         return;
 
-    if (!m_propertySet) {
-        // FIXME: This is not entirely correct. If the doctype is XHTML MP, or there is a Meta
-        // element for setting the viewport, the viewport arguments should fall back to those
-        // settings when the @viewport rules are all removed. For now, reset to implicit when
-        // there was an @viewport rule which has now been removed.
-        if (m_document->viewportArguments().type == ViewportArguments::CSSDeviceAdaptation) {
+    if (!m_hasAuthorStyle && (m_document->useLegacyViewportArguments() || !m_propertySet)) {
+        if (!m_propertySet)
             m_document->setViewportArguments(ViewportArguments());
-            m_document->updateViewportArguments();
-        }
+        else
+            m_propertySet = 0;
         return;
     }
 
-    ViewportArguments arguments(ViewportArguments::CSSDeviceAdaptation);
+    ASSERT(m_propertySet);
+
+    ViewportArguments arguments(m_hasAuthorStyle ? ViewportArguments::CSSDeviceAdaptation : ViewportArguments::UserAgent);
 
     arguments.userZoom = getViewportArgumentValue(CSSPropertyUserZoom);
     arguments.zoom = getViewportArgumentValue(CSSPropertyZoom);
@@ -103,9 +102,9 @@ void ViewportStyleResolver::resolve()
     arguments.orientation = getViewportArgumentValue(CSSPropertyOrientation);
 
     m_document->setViewportArguments(arguments);
-    m_document->updateViewportArguments();
 
     m_propertySet = 0;
+    m_hasAuthorStyle = false;
 }
 
 float ViewportStyleResolver::getViewportArgumentValue(CSSPropertyID id) const