This fixes a small inconsistency when the accessor is on a prototype,
because the property access has to respect the holder (and not always go
to the receiver unconditionally).

R=jarin@chromium.org
BUG=v8:4470
LOG=n

Review URL: https://codereview.chromium.org/1409273005

Cr-Commit-Position: refs/heads/master@{#31375}