Derive synthetic type bounds for expressions

Currently synthesizes Smi as the lower bound for numeric operations (except for +, which might result in a string). That would need to change in places where we want to track constants as type feedback.

Does not do anything about variables yet.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/17842004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15422 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/typing.h

@@ -68,6 +68,12 @@ class AstTyper: public AstVisitor {
   void MergeUpperType(Expression* e, Handle<Type> t) {
     e->set_upper_type(handle(Type::Intersect(e->upper_type(), t), isolate_));
   }
+  void MergeLowerType(Expression* e, Type* t) {
+    MergeLowerType(e, handle(t, isolate_));
+  }
+  void MergeUpperType(Expression* e, Type* t) {
+    MergeUpperType(e, handle(t, isolate_));
+  }
 
   void VisitDeclarations(ZoneList<Declaration*>* declarations);
   void VisitStatements(ZoneList<Statement*>* statements);