This is in preparation of adding more data to the preparse record.
Using a collector instead of a list avoids copying data when the backing
store grows.

Review URL: http://codereview.chromium.org/3153037

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5334 ce2b1a6d-e550-0410-aec6-3dcde31c8c00