The Object.getOwnPropertyNames method always calls into C++ anyway,
so there's no point in having the JavaScript wrapper around at all.

Drive-by-fix: Inline GetOwnEnumerablePropertyNames into its single
call site.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1605803002

Cr-Commit-Position: refs/heads/master@{#33380}