CrossSiteDocumentResourceHandler records a number of SiteIsolation.XSD.* histograms.  This class isn't used when the network service is enabled, so all these histograms won't be recorded.  In addition to porting the logic behind CrossSiteDocumentResourceHandler to work when the NetworkService is enabled, we should either remove these histograms, or create new versions of them that work with the network service enabled.

No idea if these histograms are important enough for this to block experimenting with the NetworkService on Canary until new versions are hooked up.