It would force us to make mjsunit.js strong-compatible, and that's too much for
now (for the upcoming features) and would have a ripple effect on other
tests. Especially debug-script.js which unships harmony features would break.

R=rossberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/930293002

Cr-Commit-Position: refs/heads/master@{#26694}