Start pulling pub from its own repo.

sdk/lib/_internal/pub/test/validator/dependency_override_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 '../../lib/src/entrypoint.dart';
-import '../../lib/src/validator.dart';
-import '../../lib/src/validator/dependency_override.dart';
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-Validator dependencyOverride(Entrypoint entrypoint) =>
-    new DependencyOverrideValidator(entrypoint);
-
-main() {
-  initConfig();
-
-  integration('invalidates a package if it has dependency overrides', () {
-    d.dir(appPath, [
-      d.pubspec({
-        "name": "myapp",
-        "dependency_overrides": {
-          "foo": "<3.0.0"
-        }
-      })
-    ]).create();
-
-    expectValidationError(dependencyOverride);
-  });
-}