Set [[Writable]] to false for the "name" property of strict
functions as well, mirroring what non-strict functions have
it as.

LOG=N
R=rossberg@chromium.org
TEST=mjsunit/regress/regress-270142
BUG=270142

Review URL: https://codereview.chromium.org/99203006

Patch from Sigbjorn Finne <sigbjornf@opera.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18387 ce2b1a6d-e550-0410-aec6-3dcde31c8c00