client: expose constructor on fields for testing
client: expose constructor on fields for testing

Summary: Allows users to easily mock out a QueryResponse by being able to construct the fields directly.

Reviewed By: chadaustin

Differential Revision: D36460568

fbshipit-source-id: c32d0fab265225d11307722a2895e2c6e3a5f37e

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman