Compute [WorldImpact] for main method as entrypoint

tests/compiler/dart2js/kernel/closed_world_test.dart

 // Copyright (c) 2016, 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.
 
 // Tests that the closed world computed from [WorldImpact]s derived from kernel
 // is equivalent to the original computed from resolution.
 library dart2js.kernel.closed_world_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/commandline_options.dart';
@@ skipping 26 matching lines @@
 abstract class B implements A {
   factory B.a() => null;
 }
 class C implements B {
   // redirecting factory in concrete to other class
   factory C.a() = D.a;
 }
 class D implements C {
   D.a();
 }
-main() {
+main(args) {
   new A.a();
   new A.b();
   new C.a();
   print(new List<String>()..add('Hello World!'));
 }
 '''
 };
 
 main(List<String> args) {
   Arguments arguments = new Arguments.from(args);
@@ skipping 37 matching lines @@
         backend,
         compiler.commonElements,
         compiler.cacheStrategy,
         'enqueuer from kernel');
     // TODO(johnniwinther): Store backend info separately. This replacement is
     // made to reset a field in [TypeVariableHandler] that prevents it from
     // enqueuing twice.
     backend.typeVariableHandler = new TypeVariableHandler(compiler);
 
     backend.enqueueHelpers(enqueuer);
-    enqueuer.addToWorkList(compiler.mainFunction);
+    enqueuer.applyImpact(
+        compiler.impactStrategy,
+        enqueuer.nativeEnqueuer
+            .processNativeClasses(compiler.libraryLoader.libraries));
+    enqueuer.applyImpact(compiler.impactStrategy,
+        backend.computeMainImpact(enqueuer, compiler.mainFunction));
     enqueuer.forEach((work) {
       AstElement element = work.element;
       ResolutionImpact resolutionImpact = build(compiler, element.resolvedAst);
       WorldImpact worldImpact = compiler.backend.impactTransformer
           .transformResolutionImpact(enqueuer, resolutionImpact);
       enqueuer.registerProcessedElement(element);
       enqueuer.applyImpact(compiler.impactStrategy, worldImpact,
           impactSource: element);
     });
     ClosedWorld closedWorld =
@@ skipping 15 matching lines @@
         }
         // The class cannot itself be instantiated.
         return false;
       }
       return true;
     }, verbose: arguments.verbose);
     checkClosedWorlds(compiler.closedWorld, closedWorld,
         verbose: arguments.verbose);
   });
 }