Function proxies would not be printed so far since they ended up in Function.prototype.toString which only works with Function as a receiver but no Proxy. Additionally added support for more gracefully dealing with recursive __proto__ structures introduced by proxies.

drive-by-fix: use IS_PROXY if possible in .js files.

BUG=v8:1543
LOG=n

Committed: https://crrev.com/8bfb7189a3472bc9d0820a1bd4534eaaf78ff847
Cr-Commit-Position: refs/heads/master@{#32985}

Review URL: https://codereview.chromium.org/1530293004

Cr-Commit-Position: refs/heads/master@{#33010}