Function inlining no longer uses subgraphs.  We detect inlining in an
effect context and avoid materializing a return value earlier than we
did before.

Review URL: http://codereview.chromium.org/6635012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7080 ce2b1a6d-e550-0410-aec6-3dcde31c8c00