[IndexedDB] Pool and evict leveldb iterators, to save memory

content/browser/indexed_db/leveldb/leveldb_iterator_pool_controller.h

+// Copyright 2017 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 CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_ITERATOR_POOL_CONTROLLER_H_
+#define CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_ITERATOR_POOL_CONTROLLER_H_
+
+#include <memory>
+
+namespace leveldb {
+class Iterator;
+class Snapshot;
+}
+
+namespace content {
+class LevelDBIterator;
+
+class LevelDBIteratorPoolController {
+ public:
+  virtual ~LevelDBIteratorPoolController() {}
+
+  virtual std::unique_ptr<leveldb::Iterator> CreateLevelDBIterator(
+      const leveldb::Snapshot*) = 0;
+  virtual void NotifyIteratorUsed(LevelDBIterator*) = 0;
+  virtual void NotifyIteratorDestroyed(LevelDBIterator*) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_ITERATOR_POOL_CONTROLLER_H_