Fixes for re-enabling more MSVC level 4 warnings: angle/ edition

This contains fixes for the following sorts of issues:
* Signedness mismatch

BUG=81439
TEST=none

Change-Id: Ief116d4b79b63479641259119246bb1465bbfd1f
Reviewed-on: https://chromium-review.googlesource.com/207418
Reviewed-by: Alok Priyadarshi <alokp@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
1 file changed