The release build was complaining about a missing size_t definition
in blocklayout.h.

BUG=angle:568

Change-Id: I9757f3ac45627a2a73d4f90cc507f8620674820e
Reviewed-on: https://chromium-review.googlesource.com/196290Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>