Fix and enable warning C4245 (signed/unsigned mismatch) Change-Id: If48043835fcc98341a0626e3ece7d0e3f7958059 Reviewed-on: https://chromium-review.googlesource.com/260630 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cooper Partin <coopp@microsoft.com> Tested-by: Austin Kinross <aukinros@microsoft.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>