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diff --git a/xfa/fde/css/cfde_cssaccelerator.h b/xfa/fde/css/cfde_cssaccelerator.h
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+++ b/xfa/fde/css/cfde_cssaccelerator.h
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+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#ifndef XFA_FDE_CSS_CFDE_CSSACCELERATOR_H_
+#define XFA_FDE_CSS_CFDE_CSSACCELERATOR_H_
+
+#include <memory>
+#include <stack>
+
+#include "xfa/fde/css/cfde_csstagcache.h"
+
+class CXFA_CSSTagProvider;
+
+class CFDE_CSSAccelerator {
+ public:
+  CFDE_CSSAccelerator();
+  ~CFDE_CSSAccelerator();
+
+  void OnEnterTag(CXFA_CSSTagProvider* pTag);
+  void OnLeaveTag(CXFA_CSSTagProvider* pTag);
+
+  void Clear() {
+    std::stack<std::unique_ptr<CFDE_CSSTagCache>> tmp;
+    stack_.swap(tmp);
+  }
+
+  CFDE_CSSTagCache* top() const {
+    if (stack_.empty())
+      return nullptr;
+    return stack_.top().get();
+  }
+
+ private:
+  std::stack<std::unique_ptr<CFDE_CSSTagCache>> stack_;
+};
+
+#endif  // XFA_FDE_CSS_CFDE_CSSACCELERATOR_H_