The proxy may be on its own target's or handler's prototype chain, leading
to infinite recursion either when looking up the trap, or when calling
through to the target.
We can't eagerly prevent this from happening (e.g. at "foo.__proto__ = bar"
calling time) because the presence of traps can change at any time.

BUG=v8:1543,chromium:569882
LOG=n

Review URL: https://codereview.chromium.org/1526953002

Cr-Commit-Position: refs/heads/master@{#32872}