Add model test of CodegenWorldBuilder to compile_from_dill_test

pkg/compiler/lib/src/enqueue.dart

Index: pkg/compiler/lib/src/enqueue.dart
diff --git a/pkg/compiler/lib/src/enqueue.dart b/pkg/compiler/lib/src/enqueue.dart
index a0ea7811a70f1e79864067b36e43b9ebdb293370..3b8224567bfff4e7836eb28c0b1d61a043ec15ef 100644
--- a/pkg/compiler/lib/src/enqueue.dart
+++ b/pkg/compiler/lib/src/enqueue.dart
@@ -16,6 +16,7 @@ import 'options.dart';
 import 'elements/entities.dart';
 import 'elements/resolution_types.dart' show ResolutionTypedefType;
 import 'elements/types.dart';
+import 'js_backend/enqueuer.dart';
 import 'universe/world_builder.dart';
 import 'universe/use.dart'
     show
@@ -33,6 +34,7 @@ import 'world.dart' show ClosedWorld;
 
 class EnqueueTask extends CompilerTask {
   ResolutionEnqueuer _resolution;
+  CodegenEnqueuer codegenEnqueuerForTesting;
   final Compiler compiler;
 
   String get name => 'Enqueue';
@@ -57,7 +59,8 @@ class EnqueueTask extends CompilerTask {
   }
 
   Enqueuer createCodegenEnqueuer(ClosedWorld closedWorld) {
-    return compiler.backend.createCodegenEnqueuer(this, compiler, closedWorld);
+    return codegenEnqueuerForTesting =
+        compiler.backend.createCodegenEnqueuer(this, compiler, closedWorld);
   }
 }