Fix dart2dart and dart2js build.

lib/compiler/implementation/resolved_visitor.dart

 // Copyright (c) 2012, 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 ResolvedVisitor<R> extends AbstractVisitor<R> {
   TreeElements elements;
 
   ResolvedVisitor(this.elements);
 
   R visitSend(Send node) {
     if (node.isSuperCall) {
       return visitSuperSend(node);
     } else if (node.isOperator) {
       return visitOperatorSend(node);
     } else if (node.isPropertyAccess) {
       return visitGetterSend(node);
     } else if (Elements.isClosureSend(node, elements[node])) {
       return visitClosureSend(node);
     } else {
       Element element = elements[node];
-      if (element === null) {
+      if (Element.isInvalid(element)) {
         // Example: f() with 'f' unbound.
         // This can only happen inside an instance method.
         return visitDynamicSend(node);
       } else if (element.kind == ElementKind.CLASS) {
         internalError("Cannot generate code for send", node: node);
       } else if (element.isInstanceMember()) {
         // Example: f() with 'f' bound to instance method.
         return visitDynamicSend(node);
       } else if (element.kind === ElementKind.FOREIGN) {
         return visitForeignSend(node);
@@ skipping 15 matching lines @@
   abstract R visitDynamicSend(Send node);
   abstract R visitForeignSend(Send node);
   abstract R visitStaticSend(Send node);
 
   abstract void internalError(String reason, [Node node]);
 
   R visitNode(Node node) {
     internalError("Unhandled node", node);
   }
 }