Clean up forward declarations in Source/core/css

Source/core/css/CSSSupportsRule.h

 /* Copyright (C) 2012 Motorola Mobility 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 disclaimer.
  * 2. Redistributions in binary form must reproduce the above
  *    copyright notice, this list of conditions and the following disclaimer in
@@ skipping 15 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef CSSSupportsRule_h
 #define CSSSupportsRule_h
 
 #include "core/css/CSSGroupingRule.h"
 
 namespace blink {
 
-class CSSRule;
 class StyleRuleSupports;
 
 class CSSSupportsRule FINAL : public CSSGroupingRule {
 public:
     static PassRefPtrWillBeRawPtr<CSSSupportsRule> create(StyleRuleSupports* rule, CSSStyleSheet* sheet)
     {
         return adoptRefWillBeNoop(new CSSSupportsRule(rule, sheet));
     }
 
     virtual ~CSSSupportsRule() { }
 
     virtual CSSRule::Type type() const OVERRIDE { return SUPPORTS_RULE; }
     virtual String cssText() const OVERRIDE;
 
     String conditionText() const;
 
     virtual void trace(Visitor* visitor) OVERRIDE { CSSGroupingRule::trace(visitor); }
 
 private:
     CSSSupportsRule(StyleRuleSupports*, CSSStyleSheet*);
 };
 
 DEFINE_CSS_RULE_TYPE_CASTS(CSSSupportsRule, SUPPORTS_RULE);
 
 } // namespace blink
 
 #endif // CSSSupportsRule_h