BUG=1385
TEST=Existing tests still pass; running d8 with --dump-counters shows fewer polymorphic stubs being compiled

Review URL: http://codereview.chromium.org/7094003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8183 ce2b1a6d-e550-0410-aec6-3dcde31c8c00