LayoutTests: fix cross-frame-access-enumeration

According to the html-cross-origin-objects spec, Object.keys() should return
whitelisted ("all-can-read") properties for access-restricted objects. Fix
the test to expect this behavior. Also skip it temporarily, because the
actual fix will roll in with V8.

BUG=chromium:565934

Review URL: https://codereview.chromium.org/1503453002

Cr-Commit-Position: refs/heads/master@{#363197}
3 files changed