This allows the Buffer class to always know if it's intended to
use static data vs dynamic. In some cases we would end up with
NULL pointers and not know if we started with static or dynamic
usage.

BUG=angle:912

Change-Id: I79ca62674543e0cf4b2ba9b31b6d8918723b31ce
Reviewed-on: https://chromium-review.googlesource.com/249460Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>