Remove _WorkerStub hack to make benefit closing an isolate.

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

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2505 matching lines @@
         if (cls.isNative()) hasNative = true;
       }
     }
     if (hasDouble) {
       hasNumber = true;
     }
     if (hasInt) hasNumber = true;
 
     if (classes == backend.interceptedClasses) {
       // I.e. this is the general interceptor.
-      // TODO(9556): Remove 'holders'.  The general interceptor is used on type
-      // checks and needs to handle 'native' classes for 'holders'.
-      hasNative = true;
+      hasNative = compiler.enqueuer.codegen.nativeEnqueuer.hasNativeClasses();
     }
 
     jsAst.Block block = new jsAst.Block.empty();
 
     if (hasNumber) {
       jsAst.Statement whenNumber;
 
       /// Note: there are two number classes in play: Dart's [num],
       /// and JavaScript's Number (typeof receiver == 'number').  This
       /// is the fallback used when we have determined that receiver
@@ skipping 576 matching lines @@
 """;
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;