The usage of checked numerics showed has a big hotspot in ValidateDrawAttribs.
BUG=angleproject:1671
BUG=chromium:674143

Change-Id: I96392e099b2257e465fb47e1c96f9aa1f54a89ba
Reviewed-on: https://chromium-review.googlesource.com/422428
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>