Move towards using WorldImpact for codegen

tests/compiler/dart2js/related_types.dart

 // Copyright (c) 2015, 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 related_types;
 
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/core_types.dart';
 import 'package:compiler/src/dart_types.dart';
@@ skipping 17 matching lines @@
     if (result.isSuccess) {
       checkRelatedTypes(result.compiler);
     }
   } else {
     print('Usage dart related_types.dart <entry-point>');
   }
 }
 
 /// Check all loaded libraries in [compiler] for unrelated types.
 void checkRelatedTypes(Compiler compiler) {
+  compiler.openWorld.closeWorld();
   for (LibraryElement library in compiler.libraryLoader.libraries) {
     checkLibraryElement(compiler, library);
   }
 }
 
 /// Check [library] for unrelated types.
 void checkLibraryElement(Compiler compiler, LibraryElement library) {
   library.forEachLocalMember((Element element) {
     if (element.isClass) {
       ClassElement cls = element;
@@ skipping 381 matching lines @@
   ClassElement findClass(DartType type) => type.accept(this, null);
 
   @override
   ClassElement visitType(DartType type, _) => null;
 
   @override
   ClassElement visitInterfaceType(InterfaceType type, _) {
     return type.element;
   }
 }