Implemented specialized stubs for API getters. This includes a number

Implemented specialized stubs for API getters.  This includes a number
of individual changes:

  - Added infrastructure for custom stub caching.
  - Push the code object onto the stack in exit calls instead of a
    debug/non-debug marker.
  - Remove the DEBUG_EXIT frame type.
  - Add a new exit stub generator for API getters.

Committed: http://code.google.com/p/v8/source/detail?r=3130
Review URL: http://codereview.chromium.org/330017

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3150 ce2b1a6d-e550-0410-aec6-3dcde31c8c00