Add support for pub install.

utils/pub/command_install.dart

+// Copyright (c) 2012, 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.
+
+/** Handles the `install` pub command. */
+class InstallCommand extends PubCommand {
+  String get description() => "install the current package's dependencies";
+
+  void onRun() {
+    var installedDeps = packagesDir.package.dependencies.map(

[Bob Nystrom, 2012/05/04 17:02:07]

Seems like this could be a method on PackagesDir itself. Feels a bit non-OOP to
pull out a property of packagesDir and call a method on it passing the
packagesDir back in. Maybe just do:

packagesDir.install();

[nweiz, 2012/05/07 18:28:35]

Done.

+        packagesDir.installTransitively);
+    Futures.wait(installedDeps).then((_) {
+      print('Dependencies installed!');
+    });
+  }
+}