This improves performance significantly in the Vulkan CPU overhead
test.

Bug: angleproject:2786
Change-Id: I911bc66a6b2d11dd3848ffa90927b314aeadfc24
Reviewed-on: https://chromium-review.googlesource.com/1194301
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>