Mark as prototype only after instantiating the function

BUG=
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/447293002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22979 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Enable ES6 iteration by default

This enables for-of, as well as @@iterator implementations for strings
and arrays.

R=rossberg@chromium.org
BUG=v8:2214
LOG=Y

Review URL: https://codereview.chromium.org/446023002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22980 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/master'