Log typed AST cache hit data for hover requests
Log typed AST cache hit data for hover requests

Summary: This will allow us to understand how many hover requests are hitting the typed AST cache. It will also make it easier to attribute performance improvements to the cache vs other changes.

Reviewed By: mroch

Differential Revision: D18895773

fbshipit-source-id: b5d89d7720fb0d751b5992676c29da222be08b94

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