This is a cleanup CL that is preparation for making the byte length
and offsets of typed arrays into unboxed size_t fields.

R=mstarzinger@chromium.org
BUG=v8:7881

Change-Id: Iee8bb2142124c88c71cec7343149ae3f08b40c6c
Reviewed-on: https://chromium-review.googlesource.com/1179829Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55196}