Make listDir and createSymlink synchronous in pub.

utils/pub/path_source.dart

 // Copyright (c) 2013, 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 path_source;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:pathos/path.dart' as path;
@@ skipping 29 matching lines @@
   }
 
   Future<bool> install(PackageId id, String destination) {
     return defer(() {
       try {
         _validatePath(id.name, id.description);
       } on FormatException catch(err) {
         return false;
       }
 
-      return createPackageSymlink(id.name, id.description["path"], destination,
+      createPackageSymlink(id.name, id.description["path"], destination,
           relative: id.description["relative"]);
-    }).then((_) => true);
+      return true;
+    });
   }
 
   /// Parses a path dependency. This takes in a path string and returns a map.
   /// The "path" key will be the original path but resolved relative to the
   /// containing path. The "relative" key will be `true` if the original path
   /// was relative.
   ///
   /// A path coming from a pubspec is a simple string. From a lock file, it's
   /// an expanded {"path": ..., "relative": ...} map.
   dynamic parseDescription(String containingPath, description,
@@ skipping 47 matching lines @@
 
     if (fileExists(dir)) {
       throw new FormatException(
           "Path dependency for package '$name' must refer to a "
           "directory, not a file. Was '$dir'.");
     }
 
     throw new FormatException("Could not find package '$name' at '$dir'.");
   }
 }