Const variables are not considered as trivial sub-expressions since
we have the check for the hole value as a side-effect.

Review URL: http://codereview.chromium.org/849003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4112 ce2b1a6d-e550-0410-aec6-3dcde31c8c00