Tweaks to improve field_ref compile time
Tweaks to improve field_ref compile time

Summary: [Thrift] Tweaks to improve `field_ref` compile time.

Reviewed By: Mizuchi

Differential Revision: D22038083

fbshipit-source-id: 7689ab5e00abc48e2ffb484220e66e7ad0b44538

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift