Start resolving classes and default constructors.

frog/leg/typechecker.dart

Index: frog/leg/typechecker.dart
===================================================================
--- frog/leg/typechecker.dart	(revision 2023)
+++ frog/leg/typechecker.dart	(working copy)
@@ -340,6 +340,11 @@
     return types.dynamicType;
   }
 
+  Type visitNewExpression(NewExpression node) {
+    // TODO(karlklose): return the type.
+    return types.dynamicType;
+  }
+
   Type visitLiteralList(LiteralList node) {
     return types.dynamicType;
   }