Introduce HistoryClient interface

components/history/core/browser/history_client.h

+// 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_HISTORY_CORE_BROWSER_HISTORY_CLIENT_H_
+#define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_CLIENT_H_
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+namespace history {
+
+// This class abstracts operations that depend on the embedder's environment,
+// e.g. Chrome.
+class HistoryClient : public KeyedService {
+ protected:
+  HistoryClient() {}
+
+  DISALLOW_COPY_AND_ASSIGN(HistoryClient);
+};
+
+}  // namespace history
+
+#endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_CLIENT_H_