Add optional message to assert in Dart2js.

pkg/compiler/lib/src/closure.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.
 
 library closureToClassMapper;
 
 import 'common/names.dart' show
     Identifiers;
 import 'common/tasks.dart' show
     CompilerTask;
@@ skipping 768 matching lines @@
     } else if (node.isTypeTest || node.isTypeCast) {
       TypeAnnotation annotation = node.typeAnnotationFromIsCheckOrCast;
       DartType type = elements.getType(annotation);
       analyzeType(type);
     } else if (node.isTypeTest) {
       DartType type = elements.getType(node.typeAnnotationFromIsCheckOrCast);
       analyzeType(type);
     } else if (node.isTypeCast) {
       DartType type = elements.getType(node.arguments.head);
       analyzeType(type);
-    } else if (elements.isAssert(node) && !compiler.enableUserAssertions) {
-      return;
     }
     node.visitChildren(this);
   }
 
   visitSendSet(SendSet node) {
     Element element = elements[node];
     if (Elements.isLocal(element)) {
       mutatedVariables.add(element);
       if (compiler.enableTypeAssertions) {
         TypedElement typedElement = element;
@@ skipping 321 matching lines @@
 
   String get name => typeVariable.name;
 
   int get hashCode => typeVariable.hashCode;
 
   bool operator ==(other) {
     if (other is! TypeVariableLocal) return false;
     return typeVariable == other.typeVariable;
   }
 }