Disallow copying of the MemoryBuffer class. BUG=angle:836 Change-Id: Ie3f674ef6c321770209a37b1af06ea21d788f476 Reviewed-on: https://chromium-review.googlesource.com/231232 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>