c36db8f9e1
According to the Pernosco trace, https://static.pernos.co/server/7c640bc4ed587e824fab0ca8aa44f41d1b5595b5/rebuilding.html?redirect=https%3A%2F%2Fpernos.co%2Fdebug%2FAKTDVC62g_oHMo8GmtoA1g%2Findex.html, this is a case that the propagated BrowingContext has been discarded already, so it causes aBrowsingContext.GetMaybeDiscarded() get a nullptr. This patch just check if the propageted BrowsingContext is discarded. For the discarded BrowsingContext, try to use its BrowsingContextId to get the corresponding CanonicalBrowsingContext instead of using the propagated one. Differential Revision: https://phabricator.services.mozilla.com/D237702