This CL fixes a long-standing bug with Object.keys where the enumerability
check was omitted if the [ownKeys] trap is not present. The only distinction the
KeyAccumulator needs is whether it collects keys for for-in (is_for_in_) or not.
ForInFilter performs a separate step to filter out non-enumerable keys later-on
while in all the other use-cases we have to filter keys.
BUG=v8:1543, v8:5250
Review-Url: https://codereview.chromium.org/2176113009
Cr-Commit-Position: refs/heads/master@{#38199}
Both of them shipped in Chrome 49 without incident.
Also move relevant tests from harmony/ to es6/.
Review URL: https://codereview.chromium.org/1815773002
Cr-Commit-Position: refs/heads/master@{#34964}