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

Source/core/css/RuleSet.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 375 matching lines @@
         } else if (rule->isRegionRule() && resolver) {
             // FIXME (BUG 72472): We don't add @-webkit-region rules of scoped style sheets for the moment.
             addRegionRule(static_cast<StyleRuleRegion*>(rule), hasDocumentSecurityOrigin);
         } else if (rule->isHostRule() && resolver) {
             if (!isScopingNodeInShadowTree(scope))
                 continue;
             bool enabled = resolver->buildScopedStyleTreeInDocumentOrder();
             resolver->setBuildScopedStyleTreeInDocumentOrder(false);
             resolver->ensureScopedStyleResolver(scope->shadowHost())->addHostRule(static_cast<StyleRuleHost*>(rule), hasDocumentSecurityOrigin, scope);
             resolver->setBuildScopedStyleTreeInDocumentOrder(enabled);
-        } else if (RuntimeEnabledFeatures::cssViewportEnabled() && rule->isViewportRule()) {
+        } else if (rule->isViewportRule()) {
             // @viewport should not be scoped.
             if (!isDocumentScope(scope))
                 continue;
             addViewportRule(static_cast<StyleRuleViewport*>(rule));
         }
         else if (rule->isSupportsRule() && static_cast<StyleRuleSupports*>(rule)->conditionIsSupported())
             addChildRules(static_cast<StyleRuleSupports*>(rule)->childRules(), medium, resolver, scope, hasDocumentSecurityOrigin, addRuleFlags);
     }
 }
 
@@ skipping 48 matching lines @@
     compactPendingRules(pendingRules->shadowPseudoElementRules, m_shadowPseudoElementRules);
     m_linkPseudoClassRules.shrinkToFit();
     m_cuePseudoRules.shrinkToFit();
     m_focusPseudoClassRules.shrinkToFit();
     m_universalRules.shrinkToFit();
     m_pageRules.shrinkToFit();
     m_viewportRules.shrinkToFit();
 }
 
 } // namespace WebCore