Add offline support to pub install and update.

sdk/lib/_internal/pub/bin/pub.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.
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:args/args.dart';
 import 'package:pathos/path.dart' as path;
@@ skipping 73 matching lines @@
   if (Platform.environment.containsKey('PUB_CACHE')) {
     cacheDir = Platform.environment['PUB_CACHE'];
   } else if (Platform.operatingSystem == 'windows') {
     var appData = Platform.environment['APPDATA'];
     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 = PubCommand.commands[globalOptions.rest[0]];
     if (command == null) {
       log.error('Could not find a command named "${globalOptions.rest[0]}".');
       log.error('Run "pub help" to see available commands.');
       exit(exit_codes.USAGE);
       return;
     }
 
     var commandArgs = globalOptions.rest.sublist(1);
-    command.run(cache, globalOptions, commandArgs);
+    command.run(cacheDir, globalOptions, commandArgs);
   });
 }
 
 /// Checks that pub is running on a supported platform. If it isn't, it prints
 /// an error message and exits. Completes when the validation is done.
 Future validatePlatform() {
   return new Future.sync(() {
     if (Platform.operatingSystem != 'windows') return;
 
     return runProcess('ver', []).then((result) {
@@ skipping 33 matching lines @@
   for (var name in names) {
     buffer.write('  ${padRight(name, length)}   '
         '${PubCommand.commands[name].description}\n');
   }
 
   buffer.write('\n');
   buffer.write(
       'Use "pub help [command]" for more information about a command.');
   log.message(buffer.toString());
 }