Summary:
The breakage fixed by changeset [1] could have been identified earlier if we had typing on `attachHMRServer`, so I spent some time on that. This has revealed in turn a few functions across the codebase that were incorrectly typed, and that are now fixed.
[1] packager: attachHMRServer.js: fix callsite of Server#getModuleForPath()
Reviewed By: davidaurelio
Differential Revision: D4706241
fbshipit-source-id: fc4285245921ae45d5781a47d626fc0559dba998