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

utils/pub/pub.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.
 
 /// The main entrypoint for the pub command line application.
 library pub;
 
 import 'dart:async';
+import 'dart:io';
+import 'dart:math';
+
 import '../../pkg/args/lib/args.dart';
 import '../../pkg/path/lib/path.dart' as path;
-import 'dart:io';
-import 'dart:math';
-import 'http.dart';
-import 'io.dart';
+
 import 'command_help.dart';
 import 'command_install.dart';
 import 'command_lish.dart';
 import 'command_update.dart';
 import 'command_uploader.dart';
 import 'command_version.dart';
 import 'entrypoint.dart';
 import 'exit_codes.dart' as exit_codes;
+import 'http.dart';
+import 'io.dart';
 import 'log.dart' as log;
 import 'package.dart';
 import 'pubspec.dart';
 import 'sdk.dart' as sdk;
 import 'source.dart';
 import 'source_registry.dart';
 import 'system_cache.dart';
 import 'utils.dart';
 import 'version.dart';
 
@@ skipping 76 matching lines @@
       break;
   }
 
   SecureSocket.initialize(database: relativeToPub('resource/certs'));
 
   var cacheDir;
   if (Platform.environment.containsKey('PUB_CACHE')) {
     cacheDir = Platform.environment['PUB_CACHE'];
   } else if (Platform.operatingSystem == 'windows') {
     var appData = Platform.environment['APPDATA'];
-    cacheDir = join(appData, 'Pub', 'Cache');
+    cacheDir = path.join(appData, 'Pub', 'Cache');
   } else {
     cacheDir = '${Platform.environment['HOME']}/.pub-cache';
   }
 
   validatePlatform().then((_) {
     var cache = new SystemCache.withSources(cacheDir);
 
     // Select the command.
     var command = pubCommands[globalOptions.rest[0]];
     if (command == null) {
@@ skipping 186 matching lines @@
     if (exception is HttpException || exception is HttpParserException ||
         exception is SocketIOException || exception is PubHttpException) {
       return exit_codes.UNAVAILABLE;
     } else if (exception is FormatException) {
       return exit_codes.DATA;
     } else {
       return 1;
     }
   }
 }