Move pub into sdk/lib/_internal.

utils/tests/pub/install/git/check_out_branch_test.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 pub_tests;
-
-import 'dart:io';
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('checks out a package at a specific branch from Git', () {
-    ensureGit();
-
-    var repo = d.git('foo.git', [
-      d.libDir('foo', 'foo 1'),
-      d.libPubspec('foo', '1.0.0')
-    ]);
-    repo.create();
-    repo.runGit(["branch", "old"]);
-
-    d.git('foo.git', [
-      d.libDir('foo', 'foo 2'),
-      d.libPubspec('foo', '1.0.0')
-    ]).commit();
-
-    d.appDir([{"git": {"url": "../foo.git", "ref": "old"}}]).create();
-
-    schedulePub(args: ['install'],
-        output: new RegExp(r"Dependencies installed!$"));
-
-    d.dir(packagesPath, [
-      d.dir('foo', [
-        d.file('foo.dart', 'main() => "foo 1";')
-      ])
-    ]).validate();
-  });
-}