[turbofan] Initial version of ValueNumberingReducer.

TEST=compiler-unittests,cctest,mjsunit
R=mstarzinger@chromium.org, jarin@chromium.org

Review URL: https://codereview.chromium.org/539503002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23686 ce2b1a6d-e550-0410-aec6-3dcde31c8c00