Move the CSS Device Adaptation @viewport rule support behind a runtime flag

Source/core/css/CSSViewportRule.h

 /*
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
@@ skipping 13 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
  * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #ifndef CSSViewportRule_h
 #define CSSViewportRule_h
 
-#if ENABLE(CSS_DEVICE_ADAPTATION)
-
 #include "core/css/CSSRule.h"
 
 namespace WebCore {
 
 class CSSStyleDeclaration;
 class StyleRuleViewport;
 class StyleRuleCSSStyleDeclaration;
 
 class CSSViewportRule: public CSSRule {
 public:
@@ skipping 13 matching lines @@
 private:
     CSSViewportRule(StyleRuleViewport*, CSSStyleSheet*);
 
     RefPtr<StyleRuleViewport> m_viewportRule;
     mutable RefPtr<StyleRuleCSSStyleDeclaration> m_propertiesCSSOMWrapper;
 };
 
 } // namespace WebCore
 
 #endif // CSSViewportRule_h
-
-#endif // ENABLE(CSS_DEVICE_ADAPTATION)