This fixes a corner-case in {KeyAccumulator::CollectOwnJSProxyKeys}
where the keys returned by {JSReceiver::OwnPropertyKeys} for an array
are not internalized and hence have a diverging identity from keys
returned by the "ownKeys" trap of a proxy.

R=cbruni@chromium.org
TEST=mjsunit/regress/regress-crbug-700678
BUG=chromium:700678

Change-Id: I5efd012eade14bd45c69e4abb0aeda684baf38f0
Reviewed-on: https://chromium-review.googlesource.com/452979Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43775}