addOneTab uses the existence of a referrer URI to determine where to
position the newly opened tab. Bug 1031264 changed callsites so that a
referrer URI was no longer passed in if the opening link had
rel=noreferrer set on it. This change, then, broke placement of newly
opened tabs if their opening link had rel=noreferrer on it.
Instead of not passing in the referrer URI if rel=noreferrer, let's
instead explicitly tell addOneTab whether rel=noreferrer was present on
the opening link. Then addOneTab can hide the referrer URI from the
actual network request, while still using the referrer URI to determine
tab placement.
