Private fields should not return undefined on access miss, but instead
should throw a TypeError.

This patch uses a bit on v8::Symbol to mark if this symbol is a
private field or not.

This patch also changes the LookupIterator code path that deals with
LookupIterator::State::DATA to deal with JSReceiver instead of
JSObject.

Note: the error message doesn't output the field name, but that's a
WIP.

Bug: v8:5368
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I8ae960b478eb6ae1ebf9bc90658ce3654d687977
Reviewed-on: https://chromium-review.googlesource.com/905627
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51452}