Remove _WorkerStub hack to make benefit closing an isolate.

dart/sdk/lib/_internal/compiler/implementation/compiler.dart

Index: dart/sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/compiler.dart b/dart/sdk/lib/_internal/compiler/implementation/compiler.dart
index 32a9850368c3eafd72feab305d27cafd8dbd2a04..3cc2e430caf1b518c86f55deaf9db80bb27235a8 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -725,12 +725,6 @@ abstract class Compiler implements DiagnosticListener {
     interceptorsLibrary = scanBuiltinLibrary('_interceptors');
     foreignLibrary = scanBuiltinLibrary('_foreign_helper');
     isolateHelperLibrary = scanBuiltinLibrary('_isolate_helper');
-    // The helper library does not use the native language extension,
-    // so we manually set the native classes this library defines.
-    // TODO(ngeoffray): Enable annotations on these classes.
-    ClassElement cls =
-        isolateHelperLibrary.find(const SourceString('_WorkerStub'));
-    cls.setNative('"Worker"');
 
     assertMethod = jsHelperLibrary.find(const SourceString('assertHelper'));
     identicalFunction = coreLibrary.find(const SourceString('identical'));