Add collection-iterator.js to BUILD.gn after r21615

LOG=n
BUG=none
TBR=adamk@chromium.org

Review URL: https://codereview.chromium.org/314623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21619 ce2b1a6d-e550-0410-aec6-3dcde31c8c00