Add a "global activate" command to pub.

sdk/lib/_internal/pub/test/global/activate/installs_dependencies_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 'package:scheduled_test/scheduled_test.dart';
+
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+
+main() {
+  initConfig();
+  integration('activating a package installs its dependencies too', () {
+    servePackages([
+      packageMap("foo", "1.0.0", {"bar": "any"}),
+      packageMap("bar", "1.0.0", {"baz": "any"}),
+      packageMap("baz", "1.0.0")
+    ]);
+
+    schedulePub(args: ["global", "activate", "foo"], output: allOf([
+      contains("Downloading bar 1.0.0..."),
+      contains("Downloading baz 1.0.0...")
+    ]));
+  });
+}