Implement code generation for === and !==.

frog/leg/resolver.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.
 
 class TreeElements {
   Map<Node, Element> map;
   TreeElements() : map = new LinkedHashMap<Node, Element>();
   operator []=(Node node, Element element) => map[node] = element;
   operator [](Node node) => map[node];
 }
@@ skipping 431 matching lines @@
       SourceString name = cls.name;
       constructor = cls.resolve(compiler).lookupConstructor(name);
       if (name == cls.name
           && constructor === null
           && node.send.argumentsNode.isEmpty()) {
         constructor = cls.getSynthesizedConstructor();
       }
       if (constructor === null) {
         error(node, MessageKind.CANNOT_FIND_CONSTRUCTOR, [node]);
       }
+    } else {
+      Node selector = node.send.selector;
+      error(selector, MessageKind.CANNOT_RESOLVE_TYPE, [selector]);
     }
 
     useElement(node.send, constructor);
     return null;
   }
 
   visitModifiers(Modifiers node) {
     // TODO(ngeoffray): Implement this.
     cancel(node, 'unimplemented');
   }
@@ skipping 251 matching lines @@
 class TopScope extends Scope {
   Universe universe;
 
   TopScope(Universe this.universe) : super(null, null);
   Element lookup(SourceString name) => universe.find(name);
 
   Element add(Element element) {
     throw "Cannot add an element in the top scope";
   }
 }