void RenderThreadImpl::OnSetZoomLevelForCurrentURL(const std::string& scheme,
                                                   const std::string& host,
                                                   double zoom_level) {
  RenderViewZoomer zoomer(scheme, host, zoom_level);
  RenderView::ForEach(&zoomer);
}

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.