[piexwasm] Include the image size in the malloc() failure Error

Bug: 935285
Change-Id: Id2810b266440a339f5dbbe7fd9f3814f5e24ad23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616838
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661255}