Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/install/pub_install_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS d.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 d.file.
 
 library pub_tests;
 
 import 'dart:io';
 
 import 'package:pathos/path.dart' as path;
 import 'package:scheduled_test/scheduled_test.dart';
 
-import '../../../pub/io.dart';
+import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
   group('requires', () {
     integration('a pubspec', () {
       d.dir(appPath, []).create();
 
       schedulePub(args: ['install'],
@@ skipping 277 matching lines @@
           d.dir("packages", [
             d.dir("myapp", [
               d.file('foo.dart', 'main() => "foo";')
             ])
           ])
         ])
       ]).validate();
     });
   });
 }