Also cleanup the interface, and make the parameter class/accessors
explicit to work-around the type-unsafety of OpParameter<T>.

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

Review URL: https://codereview.chromium.org/613683002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24322 ce2b1a6d-e550-0410-aec6-3dcde31c8c00