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>