void MediaSourceRegistry::unregisterURL(const KURL& url)
{
    DCHECK(isMainThread());
    PersistentHeapHashMap<String, Member<MediaSource>>::iterator iter = m_mediaSources.find(url.getString());
    if (iter == m_mediaSources.end())
        return;

    MediaSource* source = iter->value;
    m_mediaSources.remove(iter);
    source->removedFromRegistry();
}