It was included accidentally. It is not in the ES spec, nor is it
provided by any other browser.

BUG=chromium:793095

Change-Id: I2370a6d2b8d14def8dbd47ff4a1ffb4f5f65f097
Reviewed-on: https://chromium-review.googlesource.com/815757
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50491}