Currently we fail to properly handle shadowed properties. If the
receiver defines a non-enumerable property that reappears on the
prototype as enumerable it incorrectly shows up in [[Enumerate]].
By extending the KeyAccumulator to track non-enumerable properties
we can now properly filter them out when seeing them further up in
the prototype-chain.

BUG=v8:705
LOG=y

Review URL: https://codereview.chromium.org/1608523002

Cr-Commit-Position: refs/heads/master@{#33405}