Refactor draw validation functions. We use a significant amount of code duplication in our draw validation, that we can consolidate. BUG=angle:571 Change-Id: I96787cbddf00d9289e368456fb85079d8acec513 Reviewed-on: https://chromium-review.googlesource.com/202975 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>