ims: move InMemoryStorage from util/

refs #3940

Change-Id: I4468fe9b65ef6263a62800701eb6b03df28fa274
diff --git a/src/ims/in-memory-storage-persistent.hpp b/src/ims/in-memory-storage-persistent.hpp
new file mode 100644
index 0000000..5920ef3
--- /dev/null
+++ b/src/ims/in-memory-storage-persistent.hpp
@@ -0,0 +1,53 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2013-2017 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_IMS_IN_MEMORY_STORAGE_PERSISTENT_HPP
+#define NDN_IMS_IN_MEMORY_STORAGE_PERSISTENT_HPP
+
+#include "in-memory-storage.hpp"
+
+namespace ndn {
+
+/** @brief Provides application cache with persistent storage, of which no replacement policy will
+ *  be employed. Entries will only be deleted by explicit application control.
+ */
+class InMemoryStoragePersistent : public InMemoryStorage
+{
+public:
+  InMemoryStoragePersistent();
+
+  explicit
+  InMemoryStoragePersistent(boost::asio::io_service& ioService);
+
+NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PROTECTED:
+  /** @brief Do nothing.
+   *
+   *  This storage is persistent, and does not support eviction.
+   *
+   *  @return false
+   */
+  bool
+  evictItem() override;
+};
+
+} // namespace ndn
+
+#endif // NDN_IMS_IN_MEMORY_STORAGE_PERSISTENT_HPP