generator, mimicing the behavior of the optimizing compiler.

Initialization blocks can only contain (thus begin and end) with a
property assignment in toplevel code.

Review URL: http://codereview.chromium.org/348038

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3198 ce2b1a6d-e550-0410-aec6-3dcde31c8c00