Although it’s been whispered about since late last year, two separate sources say that a widely rumored and record-breaking Hollywood Hills real estate transaction will officially close today. Two side-by-side, shockingly expensive new homes on Robin Drive in the Bird Streets neighborhood — one of them last listed at $52 million, the other at $42.5 million — are being sold together, in a single eye-popping deal, to the same billionaire buyer.