Implement simple dynamic type check.

lib/compiler/implementation/ssa/tracer.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('tracer');
 
 #import('dart:io');
 #import('ssa.dart');
 #import('../leg.dart');
 
@@ skipping 415 matching lines @@
     // The last input is the guarded expression.
     for (int i = 0; i < inputs.length - 1; i++) {
       envBuffer.add(" ${temporaryId(inputs[i])}");
     }
     String on = node.isOn ? "on" : "off";
     String id = temporaryId(node.guarded);
     return "TypeGuard($on): $id is $type env: $envBuffer";
   }
 
   String visitIs(HIs node) {
-    String type = node.typeName.toString();
+    String type = node.typeExpression.toString();
     return "TypeTest: ${temporaryId(node.expression)} is $type";
   }
 }