Add syntax checker for side-effect-free expressions to AstOptimizer in rewriter.cc.  Add bit fields for syntax checker results to Expression in ast.h.
Review URL: http://codereview.chromium.org/660372

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3998 ce2b1a6d-e550-0410-aec6-3dcde31c8c00