Add string pools to save storage.

core/fxcrt/include/cfx_string_pool_template.h

+// Copyright 2016 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 CORE_FXCRT_INCLUDE_CFX_STRING_POOL_TEMPLATE_H_
+#define CORE_FXCRT_INCLUDE_CFX_STRING_POOL_TEMPLATE_H_
+
+#include <unordered_set>
+
+#include "core/fxcrt/include/fx_string.h"
+
+template <typename StringType>
+class CFX_StringPoolTemplate {
+ public:
+  StringType Intern(const StringType& str) { return *m_Pool.insert(str).first; }
+  void Clear() { m_Pool.clear(); }
+
+ private:
+  std::unordered_set<StringType> m_Pool;
+};
+
+using CFX_ByteStringPool = CFX_StringPoolTemplate<CFX_ByteString>;
+using CFX_WideStringPool = CFX_StringPoolTemplate<CFX_WideString>;
+
+extern template class CFX_StringPoolTemplate<CFX_ByteString>;
+extern template class CFX_StringPoolTemplate<CFX_WideString>;
+
+#endif  // CORE_FXCRT_INCLUDE_CFX_STRING_POOL_TEMPLATE_H_