Update pub to use the new command runner API in args.

sdk/lib/_internal/pub_generated/lib/src/command/downgrade.dart

Index: sdk/lib/_internal/pub_generated/lib/src/command/downgrade.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/command/downgrade.dart b/sdk/lib/_internal/pub_generated/lib/src/command/downgrade.dart
index fd38854c7e21d2ec9164a61d6f8ac9243b8929d1..87364022c3866314c03ccc690a74e75a7f95a49a 100644
--- a/sdk/lib/_internal/pub_generated/lib/src/command/downgrade.dart
+++ b/sdk/lib/_internal/pub_generated/lib/src/command/downgrade.dart
@@ -12,35 +12,35 @@ import '../solver/version_solver.dart';
 
 /// Handles the `downgrade` pub command.
 class DowngradeCommand extends PubCommand {
+  String get name => "downgrade";
   String get description =>
       "Downgrade the current package's dependencies to oldest versions.\n\n"
           "This doesn't modify the lockfile, so it can be reset with \"pub get\".";
-  String get usage => "pub downgrade [dependencies...]";
-  bool get takesArguments => true;
+  String get invocation => "pub downgrade [dependencies...]";
 
-  bool get isOffline => commandOptions['offline'];
+  bool get isOffline => argResults['offline'];
 
   DowngradeCommand() {
-    commandParser.addFlag(
+    argParser.addFlag(
         'offline',
         help: 'Use cached packages instead of accessing the network.');
 
-    commandParser.addFlag(
+    argParser.addFlag(
         'dry-run',
         abbr: 'n',
         negatable: false,
         help: "Report what dependencies would change but don't change any.");
   }
 
-  Future onRun() {
+  Future run() {
     final completer0 = new Completer();
     scheduleMicrotask(() {
       try {
-        var dryRun = commandOptions['dry-run'];
+        var dryRun = argResults['dry-run'];
         new Future.value(
             entrypoint.acquireDependencies(
                 SolveType.DOWNGRADE,
-                useLatest: commandOptions.rest,
+                useLatest: argResults.rest,
                 dryRun: dryRun)).then((x0) {
           try {
             x0;