Avoid reflect_type_class in populator
Avoid reflect_type_class in populator

Summary: [Thrift] Avoid `reflect_type_class` in `populator`; now support only calls over structure or variant types.

Reviewed By: Mizuchi

Differential Revision: D24823581

fbshipit-source-id: 5cc9e6f57189c89c442dcd567f8bc2868d0bc521

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