Use args' command support for pub commands.

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 a57886f8d8e778e5a246b6150200e45a104ee3c5..afc9d2f88aefb84f902418cc95686853bab9d574 100644
--- a/sdk/lib/_internal/pub/lib/src/command_install.dart
+++ b/sdk/lib/_internal/pub/lib/src/command_install.dart
@@ -17,14 +17,13 @@ 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'];
 
+  InstallCommand() {
+    commandParser.addFlag('offline',
+        help: 'Use cached packages instead of accessing the network.');
+  }
+
   Future onRun() {
     return entrypoint.installDependencies()
         .then((_) => log.message("Dependencies installed!"));