Introduce TabRestoreServiceClient and //chrome implementation.

components/sessions/core/session_constants.h

+// Copyright 2015 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_SESSIONS_CORE_SESSION_CONSTANTS_H_
+#define COMPONENTS_SESSIONS_CORE_SESSION_CONSTANTS_H_
+
+#include "components/sessions/sessions_export.h"
+
+namespace sessions {
+
+// The maximum number of navigation entries in each direction to persist.
+extern const int SESSIONS_EXPORT gMaxPersistNavigationCount;
+
+}  // namespace sessions
+
+#endif  // COMPONENTS_SESSIONS_CORE_SESSION_CONSTANTS_H_