Implement type visiting for uses
Implement type visiting for uses

Summary: In my next diff context optimizer can reach uses. Because the context optimizer could not reach uses before uses could not be visited. Instead they called out to `__TODO__`. However, now that context optimizer can reach uses we must visit them so that context optimizer can find everything we need.

Reviewed By: avikchaudhuri

Differential Revision: D5711864

fbshipit-source-id: 2f8260352af51fafc858371768ec0f158f3b1068

gabelevi/flow,gabelevi/flow,mroch/flow,jamesgpearce/flow,samwgoldman/flow,facebook/flow,popham/flow,samwgoldman/flow,samwgoldman/flow,ylu1317/flow,claudiopro/flow,nmote/flow,samwgoldman/flow,AgentME/flow,TiddoLangerak/flow,mroch/flow,JonathanUsername/flow,JonathanUsername/flow,mroch/flow,mroch/flow,ylu1317/flow,samwgoldman/flow,nmote/flow,mroch/flow,facebook/flow,claudiopro/flow,gabelevi/flow,claudiopro/flow,AgentME/flow,samwgoldman/flow,mroch/flow,ylu1317/flow,AgentME/flow,jamesgpearce/flow,MichaelDeBoey/flow,jamesgpearce/flow,TiddoLangerak/flow,gabelevi/flow,claudiopro/flow,nmote/flow,gabelevi/flow,facebook/flow,nmote/flow,TiddoLangerak/flow,facebook/flow,MichaelDeBoey/flow,JonathanUsername/flow,MichaelDeBoey/flow,AgentME/flow,popham/flow,MichaelDeBoey/flow,jamesgpearce/flow,JonathanUsername/flow,JonathanUsername/flow,popham/flow,ylu1317/flow,popham/flow,JonathanUsername/flow,JonathanUsername/flow,AgentME/flow,popham/flow,popham/flow,mroch/flow,jamesgpearce/flow,facebook/flow,jamesgpearce/flow,nmote/flow,MichaelDeBoey/flow,TiddoLangerak/flow,samwgoldman/flow,gabelevi/flow,TiddoLangerak/flow,facebook/flow,claudiopro/flow,jamesgpearce/flow,ylu1317/flow,nmote/flow,nmote/flow,facebook/flow,popham/flow,gabelevi/flow