Reduces draw call overhead by up to 3%.

Bug: angleproject:2966
Change-Id: Ie7ddb61b905fefe59a06a1528f0a3fde4accaf74
Reviewed-on: https://chromium-review.googlesource.com/c/1333608Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>