Port r9846 (4cd055a).

Original commit message:

Since we already have only one LIR class, it does not make much sense to separate them at the HIR level.

BUG=
TEST=
Review URL: http://codereview.chromium.org/8432010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9859 ce2b1a6d-e550-0410-aec6-3dcde31c8c00