accesses (eg, parameters, locals, and the expression stack elements)
and mutation (pushes and pops) go through the virtual frame.

The frame initially contains no state, and directly emits instructions
in the obvious way.  It is not currently used for deferred code.
Review URL: http://codereview.chromium.org/7076

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@489 ce2b1a6d-e550-0410-aec6-3dcde31c8c00