This was changed to match Annex B.2.5.1 of ES2015 and Firefox in
https://chromium.googlesource.com/v8/v8/+/469d9bfa, but website
breakage was seen in M49 Beta. JSC still returns undefined here.

BUG=chromium:585775
LOG=y
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1714903004

Cr-Commit-Position: refs/heads/master@{#34172}