Consider treating Service Workers as first parties

[biancadanforth]

It's not clear right now how the capture code treats Service Workers (these load in non-visible tabs, i.e. tabId = -1). It would be good to check, and we should consider treating them as first parties.

@jonathanKingston Aren't SWs usually (if not always) a same origin page script loaded from the first party? In that case any third party requests it may make would be captured relative to the page that loaded the SW, no? Are you suggesting SWs be treated as a first party separate from the page that loaded the SW? Anyway, more clarification on what this means and how we might check for it would be helpful!