Also includes a ToLower string helper for a VS2017 warning fix.

https://chromium.googlesource.com/external/gyp.git/+log/aae1e3efb50786df2..c6f471687407bf28d

BUG=angleproject:1569

Change-Id: Iaf8a091a24d937db3adb242f05c8a5c9d2b03b0f
Reviewed-on: https://chromium-review.googlesource.com/659219Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>