Look up the correct constructor for default classes.

lib/compiler/implementation/elements/elements.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('elements');
 
 #import('../tree/tree.dart');
 #import('../scanner/scannerlib.dart');
 #import('../leg.dart');  // TODO(karlklose): we only need type.
 #import('../util/util.dart');
@@ skipping 807 matching lines @@
     // Filters so that [f] is only invoked with instance fields. 
     void fieldFilter(ClassElement enclosingClass, Element member) {
       if (member.isInstanceMember() && member.kind == ElementKind.FIELD) {
         f(enclosingClass, member);
       }
     }
 
     forEachMember(fieldFilter, includeBackendMembers, includeSuperMembers);
   }
 
+  bool implementsInterface(ClassElement intrface) {
+    for (Type implementedInterfaceType in allSupertypes) {
+      ClassElement implementedInterface = implementedInterfaceType.element;
+      if (implementedInterface === intrface) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   bool isInterface() => false;
   bool isNative() => nativeName != null;
   SourceString nativeName;
 }
 
 class Elements {
   static bool isLocal(Element element) {
     return ((element !== null)
             && !element.isInstanceMember()
             && !isStaticOrTopLevelField(element)
@@ skipping 168 matching lines @@
   final Node node;
   Type bound;
   Type type;
   TypeVariableElement(name, Element enclosing, this.node, this.type,
                       [this.bound])
     : super(name, ElementKind.TYPE_VARIABLE, enclosing);
   Type computeType(compiler) => type;
   Node parseNode(compiler) => node;
   toString() => "${enclosingElement.toString()}.${name.slowToString()}";
 }