File IO tested manually in a follow-up patch.

BUG=angleproject:998

Change-Id: I0bfa778d1787cdedfbf3cd68cd134477e6dcd23c
Reviewed-on: https://chromium-review.googlesource.com/274030Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>