Summary: Similar to Promise::fulfil -> setWith change, this name is a lot clearer

Test Plan: tests

Reviewed By: hans@fb.com

Subscribers: netego-diffs@, fugalh, mwa, jgehring, fuegen, folly-diffs@, tingy, jsedgwick, yfeldblum, chalfant

FB internal diff: D2013124

Tasks: 6837405

Signature: t1:2013124:1429735106:e8861925dfeb6d7f0662c1057cbcf2ad8dcf008c