Add offline support to pub install and update.

sdk/lib/_internal/pub/lib/src/command_install.dart

Index: sdk/lib/_internal/pub/lib/src/command_install.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command_install.dart b/sdk/lib/_internal/pub/lib/src/command_install.dart
index d51b553250bf101619744997cd5d29a2f8769102..a57886f8d8e778e5a246b6150200e45a104ee3c5 100644
--- a/sdk/lib/_internal/pub/lib/src/command_install.dart
+++ b/sdk/lib/_internal/pub/lib/src/command_install.dart
@@ -6,6 +6,8 @@ library command_install;
 
 import 'dart:async';
 
+import 'package:args/args.dart';
+
 import 'command.dart';
 import 'entrypoint.dart';
 import 'log.dart' as log;
@@ -15,6 +17,14 @@ class InstallCommand extends PubCommand {
   String get description => "Install the current package's dependencies.";
   String get usage => "pub install";
 
+  ArgParser get commandParser {
+    return new ArgParser()
+        ..addFlag('offline',
+            help: 'Use cached packages instead of accessing the network.');
+  }
+
+  bool get isOffline => commandOptions['offline'];
+
   Future onRun() {
     return entrypoint.installDependencies()
         .then((_) => log.message("Dependencies installed!"));