The fast-prototype test has been outsmarted by constructor inlining
because the instantiation is been correctly optimized away. Internal
state introspection about prototype turning fast was upset by that.

R=bmeurer@chromium.org
BUG=v8:4544
LOG=n

Review URL: https://codereview.chromium.org/1474763007

Cr-Commit-Position: refs/heads/master@{#32338}