canonicalize maps for object literals. JSON objects
  with the same set of properties names will then
  share the same map.
  This reduces the amount of generated code associated 
  with object literals.
- Added a flag canonicalize_object_literal_maps.
  (default true)
- Changed the format of a function's literal array.
  Only the global context is now stored in the literal prefix.

Review URL: http://codereview.chromium.org/4078

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@371 ce2b1a6d-e550-0410-aec6-3dcde31c8c00