inline Watchman.call_on_instance
inline Watchman.call_on_instance

Summary: `call_on_instance` only has one caller, and it is very specific to the use case of blocking on the persistent socket, so adding more callers doesn't make sense. inlined it.

Reviewed By: nmote

Differential Revision: D28604150

fbshipit-source-id: 0964240694946b8fb21b1bf5c80e7271a6044d85

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