In ES6 function name and length are configurable. However, the length
and name properties of the poison pill function must not be
configurable.

BUG=v8:4011
LOG=N
R=adamk@chromium.org, rossberg@chromium.org
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1061393002

Cr-Commit-Position: refs/heads/master@{#27855}