Add a "global activate" command to pub.

sdk/lib/_internal/pub/test/global/activate/empty_constraint_test.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
-library pub_tests;
-
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../../lib/src/exit_codes.dart' as exit_codes;
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
-  integration('requires the dependency to have a pubspec with a name '
-      'field', () {
-    ensureGit();
+  integration('errors if the constraint matches no versions', () {
+    servePackages([
+      packageMap("foo", "1.0.0"),
+      packageMap("foo", "1.0.1")
+    ]);
 
-    d.git('foo.git', [
-      d.libDir('foo'),
-      d.pubspec({})
-    ]).create();
-
-    d.appDir({"foo": {"git": "../foo.git"}}).create();
-
-    pubGet(error: contains('Missing the required "name" field.'),
+    schedulePub(args: ["global", "activate", "foo", ">1.1.0"],
+        error: "Package foo has no versions that match >1.1.0.",
         exitCode: exit_codes.DATA);
   });
 }