Enqueue superclasses instead of supertypes.

pkg/compiler/lib/src/common/codegen.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 dart2js.common.codegen;
 
 import '../compiler.dart' show
     Compiler;
 import '../constants/values.dart' show
     ConstantValue;
@@ skipping 31 matching lines @@
 class CodegenRegistry extends Registry {
   final Compiler compiler;
   final TreeElements treeElements;
 
   CodegenRegistry(this.compiler, this.treeElements);
 
   bool get isForResolution => false;
 
   Element get currentElement => treeElements.analyzedElement;
 
+  String toString() => 'CodegenRegistry for $currentElement';
+
   // TODO(johnniwinther): Remove this getter when [Registry] creates a
   // dependency node.
   Setlet<Element> get otherDependencies => treeElements.otherDependencies;
 
   CodegenEnqueuer get world => compiler.enqueuer.codegen;
   JavaScriptBackend get backend => compiler.backend;
 
   void registerDependency(Element element) {
     treeElements.registerDependency(element);
   }
@@ skipping 135 matching lines @@
 
   TreeElements get resolutionTree => element.resolvedAst.elements;
 
   WorldImpact run(Compiler compiler, CodegenEnqueuer world) {
     if (world.isProcessed(element)) return const WorldImpact();
 
     registry = new CodegenRegistry(compiler, resolutionTree);
     return compiler.codegen(this, world);
   }
 }