Add model test of CodegenWorldBuilder to compile_from_dill_test

tests/compiler/dart2js/kernel/compiler_helper.dart

 // Copyright (c) 2017, 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.
 
 // Partial test that the closed world computed from [WorldImpact]s derived from
 // kernel is equivalent to the original computed from resolution.
 library dart2js.kernel.compiler_helper;
 
 import 'dart:async';
 import 'dart:io';
@@ skipping 145 matching lines @@
     print('---- generate dill -----------------------------------------------');
   }
 
   Uri dillFile = Uri.parse('$entryPoint.dill');
   await generate.main([
     '--platform=out/ReleaseX64/patched_dart2js_sdk/platform.dill',
     '$entryPoint'
   ]);
 
   if (printSteps) {
-    print('---- closed world from dill $dillFile ----------------------------');
+    print('---- compile from dill $dillFile ---------------------------------');
   }
   Compiler compiler = compilerFor(
       entryPoint: dillFile,
       options: [Flags.loadFromDill]..addAll(options),
       outputProvider: compilerOutput);
   ElementResolutionWorldBuilder.useInstantiationMap = true;
   compiler.resolution.retainCachesForTesting = true;
   await compiler.run(dillFile);
   return compiler;
 }