Add offline support to pub install and update.

sdk/lib/_internal/pub/test/pub_test.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 pub_tests;
 
 import 'dart:io';
 
 import 'package:scheduled_test/scheduled_test.dart';
 
@@ skipping 82 matching lines @@
         exitCode: 64);
   });
 
   group('help', () {
     integration('shows help for a command', () {
       schedulePub(args: ['help', 'install'],
           output: '''
             Install the current package's dependencies.
 
             Usage: pub install
+            --[no-]offline    Use cached packages instead of accessing the network
             ''');
     });
 
     integration('shows help for a command', () {
       schedulePub(args: ['help', 'publish'],
           output: '''
             Publish the current package to pub.dartlang.org.
 
             Usage: pub publish [options]
             -n, --dry-run    Validate but do not publish the package                      
@@ skipping 31 matching lines @@
       // The "version" file generated on developer builds is a little funky and
       // we need to make sure we don't choke on it.
       d.dir(sdkPath, [
         d.file('version', '0.1.2.0_r16279_bobross'),
       ]).create();
 
       schedulePub(args: ['version'], output: "Pub 0.1.2+0.r16279.bobross\n");
     });
   });
 }