Get rid of join() and encapsulate File and Directory in io.dart.

utils/pub/hosted_source.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 hosted_source;
 
 import 'dart:async';
 import 'dart:io' as io;
 import 'dart:json' as json;
 import 'dart:uri';
 
 // TODO(nweiz): Make this import better.
 import '../../pkg/http/lib/http.dart' as http;
+import '../../pkg/path/lib/path.dart' as path;
+
 import 'http.dart';
 import 'io.dart';
 import 'log.dart' as log;
 import 'package.dart';
 import 'pubspec.dart';
 import 'source.dart';
 import 'source_registry.dart';
 import 'utils.dart';
 import 'version.dart';
 
@@ skipping 68 matching lines @@
   /// subdirectories then contains a subdirectory for each package installed
   /// from that site.
   Future<String> systemCacheDirectory(PackageId id) {
     var parsed = _parseDescription(id.description);
     var url = parsed.last.replaceAll(new RegExp(r"^https?://"), "");
     var urlDir = replace(url, new RegExp(r'[<>:"\\/|?*%]'), (match) {
       return '%${match[0].charCodeAt(0)}';
     });
 
     return new Future.immediate(
-        join(systemCacheRoot, urlDir, "${parsed.first}-${id.version}"));
+        path.join(systemCacheRoot, urlDir, "${parsed.first}-${id.version}"));
   }
 
   String packageName(description) => _parseDescription(description).first;
 
   bool descriptionsEqual(description1, description2) =>
       _parseDescription(description1) == _parseDescription(description2);
 
   /// Ensures that [description] is a valid hosted package description.
   ///
   /// There are two valid formats. A plain string refers to a package with the
@@ skipping 46 matching lines @@
 
     var name = description["name"];
     if (name is! String) {
       throw new FormatException("The 'name' key must have a string value.");
     }
 
     var url = description.containsKey("url") ? description["url"] : defaultUrl;
     return new Pair<String, String>(name, url);
   }
 }