Start pulling pub from its own repo.

sdk/lib/_internal/pub/test/global/activate/empty_constraint_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 '../../../lib/src/exit_codes.dart' as exit_codes;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('errors if the constraint matches no versions', () {
-    servePackages((builder) {
-      builder.serve("foo", "1.0.0");
-      builder.serve("foo", "1.0.1");
-    });
-
-    schedulePub(args: ["global", "activate", "foo", ">1.1.0"],
-        error: """
-            Package foo has no versions that match >1.1.0 derived from:
-            - pub global activate depends on version >1.1.0""",
-        exitCode: exit_codes.DATA);
-  });
-}