Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/install/path/path_is_file_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 'package:scheduled_test/scheduled_test.dart';
 
-import '../../../../pub/exit_codes.dart' as exit_codes;
+import '../../../lib/src/exit_codes.dart' as exit_codes;
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('path dependency when path is a d.file', () {
     d.dir('foo', [
       d.libDir('foo'),
       d.libPubspec('foo', '0.0.1')
     ]).create();
@@ skipping 15 matching lines @@
     // instead of a RegExp to validate, but that requires us to move the
     // stack traces out of the stderr when we invoke pub. See also: #4706.
     var escapePath = dummyPath.replaceAll(r"\", r"\\");
 
     schedulePub(args: ['install'],
         error: new RegExp("Path dependency for package 'foo' must refer to a "
                           "directory, not a file. Was '$escapePath'."),
         exitCode: exit_codes.DATA);
   });
 }