This is partially based on r21609 but that CL was incomplete.

Function name is still non writable so one has to use defineProperty
to change the actual value.

BUG=v8:3333
LOG=N
R=adamk, mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/960343002

Cr-Commit-Position: refs/heads/master@{#26924}