If a user has the ResourceLoadStatistics logic turned off, but has the ITP Debug experimental flag turned on, you can cause a crash. This is because the WebsiteDataStore for the process doesn't bother creating a ResourceLoadStatisticsStore if the statistics machinery is not running. The ITP debug flag was being blindly set without checking if the statistics store exists or not, which can cause a crash.
<rdar://problem/39287964>
Created attachment 338228 [details] Patch
Looks good to me.
Comment on attachment 338228 [details] Patch r=me
Committed r230771: <https://trac.webkit.org/changeset/230771>