Move the identification of the corresponding StatsCounter where it belongs,
namely into the Code class. Use the null pattern to signal "no inlined Smi
code". Removed a few unused counters.
Review URL: http://codereview.chromium.org/7273066

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8470 ce2b1a6d-e550-0410-aec6-3dcde31c8c00