Backend for css rule tracking

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

Index: third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp b/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..bd4629c7ef482abcc9e223f9c795eafeee195499
--- /dev/null
+++ b/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
@@ -0,0 +1,19 @@
+// 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.
+
+#include "core/css/resolver/StyleRuleUsageTracker.h"
+
+#include "core/css/StyleRule.h"
+
+namespace blink {
+
+bool StyleRuleUsageTracker::contains(StyleRule* rule) const {
+  return m_ruleList.contains(rule);
+}
+
+DEFINE_TRACE(StyleRuleUsageTracker) {
+  visitor->trace(m_ruleList);
+}
+
+}  // namespace blink