Backend for css rule tracking

third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef StyleRuleUsageTracker_h
+#define StyleRuleUsageTracker_h
+
+#include "core/css/CSSStyleRule.h"
+
+namespace blink {
+
+class StyleRule;
+
+class StyleRuleUsageTracker : public GarbageCollected<StyleRuleUsageTracker> {
+ public:
+  void track(StyleRule* rule) { m_ruleList.add(rule); }
+
+  bool contains(StyleRule*) const;
+
+  DECLARE_TRACE();
+
+ private:
+  HeapHashSet<Member<StyleRule>> m_ruleList;
+};
+
+}  // namespace blink
+
+#endif  // StyleRuleUsageTracker_h