Reland: fix compile warnings on Windows.

BUG=angleproject:882
BUG=angleproject:883

Change-Id: If4844d50d43ff9b765f64606e8f08d65a1afd9a4
Reviewed-on: https://chromium-review.googlesource.com/303431
Tryjob-Request: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>