Previously our multiplication and other operators could
do overflows, which can lead to security bugs.

BUG=chromium:637050

Change-Id: Icee22a87909e205b71bda1c5bc1627fcf5e26e90
Reviewed-on: https://chromium-review.googlesource.com/382678
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>