The OnResourceDataUseUpdate callback in PageLoadMetricsObserver does not receive any resources that are loaded by a frame whose provisional load fails (before commit). This can occur when an iframe that is currently loading has its contents docwritten. Any sub-resources loaded by the doc.write will not be reported. Presumably this is not missing many resources as this behavior is uncommon.

AdsPageLoadMetricsObserverBrowserTest.DocOverwritesNavigation tests this for PageLoadMetricsObserver::OnLoadedResource.