This gives ~23% increase in the validation-only draw call perf test.

BUG=angleproject:959

Change-Id: I384a5c4fbb1c2cd47483bd7cf4bc1d39447a99bc
Reviewed-on: https://chromium-review.googlesource.com/267750Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>