Start pulling pub from its own repo.

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

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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';
-import '../serve/utils.dart';
-
-main() {
-  initConfig();
-  integration("passes along environment constants", () {
-    d.dir(appPath, [
-      d.pubspec({
-        "name": "myapp",
-        "transformers": [{
-          "\$dart2js": {"environment": {'CONSTANT': 'true'}}
-        }]
-      }),
-      d.dir("web", [
-        d.file("main.dart", """
-void main() {
-  if (const bool.fromEnvironment('CONSTANT')) {
-    print("hello");
-  }
-}
-""")
-      ])
-    ]).create();
-
-    pubServe();
-    requestShouldSucceed("main.dart.js", contains("hello"));
-    endPubServe();
-  });
-}