Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/lish/package_creation_provides_an_error_test.dart

 // Copyright (c) 2013, 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 'dart:json' as json;
 
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:scheduled_test/scheduled_server.dart';
 
 import '../descriptor.dart' as d;
@@ skipping 19 matching lines @@
         'error': {'message': 'Your package was too boring.'}
       }));
       request.response.close();
     });
 
     expect(pub.nextErrLine(),
         completion(equals('Your package was too boring.')));
     pub.shouldExit(1);
   });
 }