Just rely on calling toString. This matches other vendor's implementations.

BUG=chromium:948257
R=dgozman@chromium.org

Change-Id: I325a12dd47712263a1ef4deee0bb2de9c4a1c656
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1545124Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60617}