Prefer using caps to system attachment limits. The caps structure can often give a lower and faster bound, as well as being more general. We should gradually move away from the implementation limits. BUG=angleproject:930 Change-Id: I979472cdb6f59c6f0cc0c80f1c29c51295872bea Reviewed-on: https://chromium-review.googlesource.com/256731 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>