Disable assertion that no longer holds.

dart/lib/compiler/implementation/resolver.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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   Type getType(TypeAnnotation annotation);
 }
 
@@ skipping 138 matching lines @@
       }
       if (isConstructor) {
         constructorElements[element] = visitor.mapping;
       }
       return visitor.mapping;
     });
   }
 
   void resolveConstructorImplementation(FunctionElement constructor,
                                         FunctionExpression node) {
-    assert(constructor.defaultImplementation === constructor);
+    if (constructor.defaultImplementation !== constructor) return;
     ClassElement intrface = constructor.enclosingElement;
     if (!intrface.isInterface()) return;
     Type defaultType = intrface.defaultClass;
     if (defaultType === null) {
       error(node, MessageKind.NO_DEFAULT_CLASS, [intrface.name]);
     }
     ClassElement defaultClass = defaultType.element;
     defaultClass.ensureResolved(compiler);
     if (defaultClass.isInterface()) {
       error(node, MessageKind.CANNOT_INSTANTIATE_INTERFACE,
@@ skipping 1923 matching lines @@
 
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) {
     return library.find(name);
   }
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
 }