[Sync] Fixing easy lint violations.

components/sync_sessions/synced_session_tracker.h

 // Copyright 2012 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_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_
 #define COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_
 
 #include <stddef.h>
 
 #include <map>
+#include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "components/sessions/core/session_id.h"
 #include "components/sessions/core/session_types.h"
 #include "components/sync_sessions/synced_session.h"
 #include "components/sync_sessions/tab_node_pool.h"
 
@@ skipping 180 matching lines @@
   // The tag for this machine's local session, so we can distinguish the foreign
   // sessions.
   std::string local_session_tag_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncedSessionTracker);
 };
 
 }  // namespace sync_sessions
 
 #endif  // COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_