Bug 1899180. If a channel is not nsIPrivateBrowsingChannel and has no load context, use the private browsing field from it's origin attributes. r=necko-reviewers,anti-tracking-reviewers,valentin

If the channel is not a nsIPrivateBrowsingChannel, and it also has no load context (eg inside svg images) then we will over write a non-zero mPrivateBrowsingId on the OriginAttributes of the channel with 0, making NS_UsePrivateBrowsing return false for the channel.

Differential Revision: https://phabricator.services.mozilla.com/D212083