Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/install/path/shared_dependency_test.dart

 // Copyright (c) 2013, 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.
 
 import 'package:pathos/path.dart' as path;
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
@@ skipping 111 matching lines @@
     schedulePub(args: ["install"],
         output: new RegExp(r"Dependencies installed!$"));
 
     d.dir(packagesPath, [
       d.dir("foo", [d.file("foo.dart", 'main() => "foo";')]),
       d.dir("bar", [d.file("bar.dart", 'main() => "bar";')]),
       d.dir("shared", [d.file("shared.dart", 'main() => "shared";')])
     ]).validate();
   });
 }