Refactor Scheduler to simplify construction of CFG from sea of nodes. Use PreEdge/Post as part of the graph tarversal, and make finding of successor projections more robust.

R=jarin@chromium.org
BUG=

Review URL: https://codereview.chromium.org/490483002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23217 ce2b1a6d-e550-0410-aec6-3dcde31c8c00