toString on JS Proxies are leaking, see this sample code:

undefined[Function.prototype.toString]
undefined[new Proxy(Function.prototype.toString, {})]

This change fixes the behavior.

Patch credits to Yusif <yusif.khudhur@gmail.com>

Change-Id: Id82a0a5c245469973452a3e6609cb91978274b8e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2739980
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73625}