message: Implement sync_session_state::Dying::bind_with_admin_token()
  This is needed to support reviving an admin token user's session, since this is
  called instead of revive_if_needed().
diff: @@ -355,6 +355,14 @@ struct sync_session_states::Dying : public SyncSession::State {
  return false;
  }
  + void bind_with_admin_token(std::unique_lock<std::mutex>& lock, SyncSession& session,
  + const std::string& admin_token,
  + const std::string& server_url) const override
  + {
  + session.advance_state(lock, waiting_for_access_token);
  + session.m_state->refresh_access_token(lock, session, admin_token, server_url);
  + }
  +
  void log_out(std::unique_lock<std::mutex>& lock, SyncSession& session) const override
  {
  session.advance_state(lock, inactive);
  