Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/args/lib/args.dart

Index: mojo/public/dart/third_party/args/lib/args.dart
diff --git a/mojo/public/dart/third_party/args/lib/args.dart b/mojo/public/dart/third_party/args/lib/args.dart
new file mode 100644
index 0000000000000000000000000000000000000000..562df446a83b70b2ee229a6567a2f7a09ddf0387
--- /dev/null
+++ b/mojo/public/dart/third_party/args/lib/args.dart
@@ -0,0 +1,9 @@
+// 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.
+
+library args;
+
+export 'src/arg_parser.dart';
+export 'src/arg_results.dart' hide newArgResults;
+export 'src/option.dart' hide newOption;