That's cleaner than having every target depending on v8 include icu
itself.

BUG=none
R=machenbach@chromium.org

Change-Id: Icaa9e8670718664041a6efe2622366c89b733f81
Reviewed-on: https://chromium-review.googlesource.com/500127Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45196}