By default --trace-hydrogen only generates the final IR (before
code generation). The other phases can be printed by specifying
them by their first letter. Currently H=HIR, L=LIR or Z=final IR (default)
are recognized.
Review URL: https://chromiumcodereview.appspot.com/9535009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10882 ce2b1a6d-e550-0410-aec6-3dcde31c8c00