[ES6 modules] Add UseCounter for preparing a module script

Bug: 594639
Change-Id: Iabb2f3780d21c0f896073e6cad6178deced61e83
Reviewed-on: https://chromium-review.googlesource.com/575797
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487432}
3 files changed