- Removes S.p.repeat from string.js
  - Adds StringPrototypeRepeat TFJ

Bug: v8:5049
Change-Id: I0b2d512bffd97dfc2c3ba6783e2e41c4db6c8faa
Reviewed-on: https://chromium-review.googlesource.com/659097
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48023}