B777 First Officer reported loss of oil quantity on the number 1 engine. The flight crew diverted and landed safely.

Narrative

I had just arrived to the cockpit to relieve the Captain after taking first break. On the changeover brief; the Captain briefed me of the situation of apparent gradual reduction in oil quantity on the #1 engine. Captain and First Officer had been documenting the oil loss for approximately 45 minutes at that point; and had initially documented a reduction in oil quantity of approximately 1 qt every 20-30 minutes. He advised us to advise him prior to any diversion or if quantity reached 6-7qts. We continued to monitor the oil loss with me as monitoring pilot; and determined that in fact we were losing oil. The checklist indicated that the primary indication of low oil quantity is high oil temp or low oil pressure. The checklist said to continue to run the engine until one of these indications; at which point the engine should be shut down. When approaching the two hour point from CP-2 (Critical Point); and approximately 2 hours from ZZZ we determined we would have zero oil by CP-2; and be approaching zero oil at ZZZ. The FO and I called the Captain after we determined a divert was likely. Captain directed us to contact Dispatch; Maintenance Control; and an Aircraft Mechanic for a SATCOM call when he arrived in the cockpit. Maintenance Control checked and verified their system had received a notification of low oil quantity. After discussing all three of us agreed a diversion to ZZZ was warranted. We obtained a clearance to ZZZ at approximately 2 hours prior to CP-2 and approximately 2 hours from ZZZ. The divert was uneventful other than observing continued reduction in oil quantity. We had zero oil quantity on final at ZZZ; but never had an indication of high oil temp or low oil pressure. The First Officer conducted an uneventful landing at ZZZ. We taxied to the International Terminal and received a gate assignment. After shut down the #1 engine increased to 4 qts; which the mechanic indicated was because the oil drained back into the sump. The mechanic began troubleshooting and soon returned to the cockpit and informed us the chip detector plug for the starter had come out; and he found it magnetically stuck to a bolt on the cowl. We had in fact been losing oil through this chip detector port. When we asked the mechanic estimated we had 20-30 min till a low pressure or low oil temp indication. This corresponded roughly with our estimate when we made the decision to abort. I would like to add that we took off with a duty extension after an aircraft change; and our takeoff occurred within 10 minutes of our CCO (Critical Crew Offtime). Though we considered the possible effects of fatigue in our decision making; I never actually felt fatigued. I received good rest and sleep prior to the trip; and I was able to sleep on my first break after takeoff.