Extract protobuf database into a new 'leveldb_proto' component

components/leveldb_proto/proto_database.h

Index: components/leveldb_proto/proto_database.h
diff --git a/components/leveldb_proto/proto_database.h b/components/leveldb_proto/proto_database.h
new file mode 100644
index 0000000000000000000000000000000000000000..34ee799eb1f1d3734c89bf034a9cb28a082627ce
--- /dev/null
+++ b/components/leveldb_proto/proto_database.h
@@ -0,0 +1,52 @@
+// Copyright 2014 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 COMPONENTS_LEVELDB_PROTO_PROTO_DATABASE_H_
+#define COMPONENTS_LEVELDB_PROTO_PROTO_DATABASE_H_
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/callback.h"
+#include "base/files/file_path.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace leveldb_proto {
+
+// Interface for classes providing persistent storage of Protocol Buffer
+// entries (T must be a Proto type extending MessageLite).
+template <typename T>
+class ProtoDatabase {
+ public:
+  typedef base::Callback<void(bool success)> InitCallback;
+  typedef base::Callback<void(bool success)> UpdateCallback;
+  typedef base::Callback<void(bool success, scoped_ptr<std::vector<T> >)>
+      LoadCallback;
+  // A list of key-value (string, T) tuples.
+  typedef std::vector<std::pair<std::string, T> > KeyEntryVector;
+
+  virtual ~ProtoDatabase() {}
+
+  // Asynchronously initializes the object. |callback| will be invoked on the
+  // calling thread when complete.
+  virtual void Init(const base::FilePath& database_dir,
+                    InitCallback callback) = 0;
+
+  // Asynchronously saves |entries_to_save| and deletes entries from
+  // |keys_to_remove| from the database. |callback| will be invoked on the
+  // calling thread when complete.
+  virtual void UpdateEntries(
+      scoped_ptr<KeyEntryVector> entries_to_save,
+      scoped_ptr<std::vector<std::string> > keys_to_remove,
+      UpdateCallback callback) = 0;
+
+  // Asynchronously loads all entries from the database and invokes |callback|
+  // when complete.
+  virtual void LoadEntries(LoadCallback callback) = 0;
+};
+
+}  // namespace leveldb_proto
+
+#endif  // COMPONENTS_LEVELDB_PROTO_PROTO_DATABASE_H_