This patch also removes the implicit recursion on phi operands,
using a loop and a worklist instead, to avoid potential stack
overflows.

R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/21065003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15952 ce2b1a6d-e550-0410-aec6-3dcde31c8c00