Move pub into sdk/lib/_internal.

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.
-
-library command_install;
-
-import 'dart:async';
-
-import 'entrypoint.dart';
-import 'log.dart' as log;
-import 'pub.dart';
-
-/// Handles the `install` pub command.
-class InstallCommand extends PubCommand {
-  String get description => "Install the current package's dependencies.";
-  String get usage => "pub install";
-
-  Future onRun() {
-    return entrypoint.installDependencies()
-        .then((_) => log.message("Dependencies installed!"));
-  }
-}