bool ResourceDispatcherHostImpl::HandleExternalProtocol(ResourceLoader* loader,
                                                        const GURL& url) {
  if (!delegate_)
    return false;

  ResourceRequestInfoImpl* info = loader->GetRequestInfo();

  if (!IsResourceTypeFrame(info->GetResourceType()))
    return false;

  const net::URLRequestJobFactory* job_factory =
      info->GetContext()->GetRequestContext()->job_factory();
  if (job_factory->IsHandledURL(url))
    return false;

  return delegate_->HandleExternalProtocol(
      url, info->GetChildID(), info->GetWebContentsGetterForRequest(),
      info->IsMainFrame(), info->GetPageTransition(), info->HasUserGesture());
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.