Pass key in register for keyed load IC

Pass key in register for keyed load IC

The calling convention for keyed load IC is changed to have the key passed both in a register (r0) and on the stack.

Next steps will be first to remove the key from the stack and then pass the receiver in a register (r1).
Review URL: http://codereview.chromium.org/1937003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4584 ce2b1a6d-e550-0410-aec6-3dcde31c8c00