dart2js: Don't emit additional precompiled file.

sdk/lib/_internal/pub/test/dart2js/outputs_deferred_libraries_test.dart

 // Copyright (c) 2014, 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.
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 const MAIN = """
@@ skipping 32 matching lines @@
     d.dir(appPath, [
       d.appPubspec(),
       d.dir('web', [
         d.file('main.dart', MAIN),
         d.file('a.dart', A),
         d.file('b.dart', B)
       ])
     ]).create();
 
     schedulePub(args: ["build"],
-        output: new RegExp(r'Built 4 files to "build".'));
+        output: new RegExp(r'Built 3 files to "build".'));
 
     d.dir(appPath, [
       d.dir('build', [
         d.dir('web', [
           d.matcherFile('main.dart.js', isNot(isEmpty)),
           d.matcherFile('main.dart.js_1.part.js', isNot(isEmpty)),
           d.matcherFile('main.dart.js_2.part.js', isNot(isEmpty)),
         ])
       ])
     ]).validate();
   });
 }