During i18n code reorg, a couple of changes for ICU 59 prep were
lost. Add them back.

See https://codereview.chromium.org/2738503008/ for the original CL.

BUG=v8:6062
TEST=v8 can be compiled with ICU 59 (hash: c28886684 ).

Change-Id: Ie19a40a9e54d0a8966dbe8e072f9afabf9e85e4f
Reviewed-on: https://chromium-review.googlesource.com/499609Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Jungshik Shin <jshin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45213}