use physical equality in Flow_ast_mapper#jsx_element_name
use physical equality in Flow_ast_mapper#jsx_element_name

Summary:
i dunno, this seems cleaner to me :-P

avoiding structural equality is a major perf optimization for Flow_ast_mapper, although in this case the element names are very shallow.

Reviewed By: samwgoldman

Differential Revision: D28120639

fbshipit-source-id: 88adc541256225bcc5719b7cef52bcb135ef6f45

facebook/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow