Add a counter for CSSKeyframesRule's anonymous indexed getter

Source/core/css/CSSKeyframesRule.h

 /*
  * Copyright (C) 2007, 2008, 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 disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 83 matching lines @@
 
     CSSRuleList* cssRules() const override;
 
     void appendRule(const String& rule);
     void deleteRule(const String& key);
     CSSKeyframeRule* findRule(const String& key);
 
     // For IndexedGetter and CSSRuleList.
     unsigned length() const;
     CSSKeyframeRule* item(unsigned index) const;
+    CSSKeyframeRule* anonymousIndexedGetter(unsigned index) const;
 
     bool isVendorPrefixed() const { return m_isPrefixed; }
     void setVendorPrefixed(bool isPrefixed) { m_isPrefixed = isPrefixed; }
 
     void styleChanged() { m_keyframesRule->styleChanged(); }
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     CSSKeyframesRule(StyleRuleKeyframes*, CSSStyleSheet* parent);
 
     virtual CSSRule::Type type() const override { return KEYFRAMES_RULE; }
 
     RefPtrWillBeMember<StyleRuleKeyframes> m_keyframesRule;
     mutable WillBeHeapVector<RefPtrWillBeMember<CSSKeyframeRule>> m_childRuleCSSOMWrappers;
     mutable OwnPtrWillBeMember<CSSRuleList> m_ruleListCSSOMWrapper;
     bool m_isPrefixed;
 };
 
 DEFINE_CSS_RULE_TYPE_CASTS(CSSKeyframesRule, KEYFRAMES_RULE);
 
 } // namespace blink
 
 #endif // CSSKeyframesRule_h