Comment 1 for bug 1499777

Also...

void mf::SessionMediator::create_buffer_stream(
    mir::protobuf::BufferStreamParameters const* request,
    mir::protobuf::BufferStream* response,
    google::protobuf::Closure* done)
{
    auto const session = weak_session.lock();

    if (session.get() == nullptr)
        BOOST_THROW_EXCEPTION(std::logic_error("Invalid application session"));

    report->session_create_surface_called(session->name());