Change typecheck_contents result when the file is skipped
Change typecheck_contents result when the file is skipped

Summary:
This happens when the input file is not a source file, for example when it is a JSON file. This changes the diff to use the Error case for this, so that we can, in later diffs, guarantee by construction that the Ok case includes type contents artifacts.

This also brings it more into alignment with `type_contents`

Reviewed By: mroch

Differential Revision: D27577172

fbshipit-source-id: 83081257e2782c1de52555ab944e79280194f3de

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