A part of a larger refactoring to clean up the draw call
validation.

BUG=angle:571

Change-Id: I0b220d68c04524a81ca11dc58e10c90e458cabde
Reviewed-on: https://chromium-review.googlesource.com/203771Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>