Combine DEBUG_BREAK and DEBUG_PREPARE_STEP_IN into one IC stub kind DEBUG_STUB, encoding DEBUG_BREAK and DEBUG_PREPARE_STEP_IN as extra ic state.

Review URL: https://chromiumcodereview.appspot.com/11821049

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13352 ce2b1a6d-e550-0410-aec6-3dcde31c8c00