Add better error checking in ConvertFileSystemURLToPathInsideCrostini

Change method API to take resulting FilePath as input pointer, and
return bool to indicate success or otherwise since it is not
guaranteed that input will always convert.

Bug: 878324
Change-Id: I17f99201c2c4b5105cceb48d6a3c0d57b80c5f7b
Reviewed-on: https://chromium-review.googlesource.com/c/1295634
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601903}
5 files changed