This is used in chromium for html attribute event handlers.

See blink layout test fast/events/event-function-toString.html

Bug: v8:4958
Change-Id: Ib3d88af834bbb62b4ccd4683eda743d92064b075
Reviewed-on: https://chromium-review.googlesource.com/837641
Commit-Queue: Josh Wolfe <jwolfe@igalia.com>
Reviewed-by: Daniel Ehrenberg <littledan@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50460}