This should slightly reduce draw call overhead.

BUG=angleproject:1898

Change-Id: I0e515bf2868f237f1d6948c12942f8cb6637c0c0
Reviewed-on: https://chromium-review.googlesource.com/707690Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>