The null constructor they had previously could be observed as crashes in
the V8 API's Object::CreationContext() method and in Object.observe.

BUG=v8:3750
LOG=n
R=arv@chromium.org, dslomov@chromium.org

Review URL: https://codereview.chromium.org/787763005

Cr-Commit-Position: refs/heads/master@{#25757}