From similar experience, I don't think the 77L would have any problem operating from DUB's 2600m runway to LAX. Providing they use the 77L, although I can't see the 77W having that much more of a problem, although it would have more pax/cargo restrictions but would still carry largely the same as a restricted 77L. Six and two threes really but it would be nice to see it happen.
According to Boeing's charts, a Boeing 777 200LR should be able to take off at sea level on a standard day fitted with GE90 115B's at MTOW in about 9200ft, so the hit for DUB-LAX would probably be negligible as it is well within the range envelope of the aircraft.