void MediaStreamCenterChromium::queryMediaStreamSources(PassRefPtr<MediaStreamSourcesQueryClient> client)
{
    if (m_private)
        m_private->queryMediaStreamSources(client);
    else {
        MediaStreamSourceVector audioSources, videoSources;
        client->didCompleteQuery(audioSources, videoSources);
    }
}
void MediaStreamCenterGStreamer::queryMediaStreamSources(PassRefPtr<MediaStreamSourcesQueryClient> client)
{
    MediaStreamSourceVector audioSources, videoSources;
    client->didCompleteQuery(audioSources, videoSources);
}