Add a [hide] argument to [ArgParser.addFlag].

pkg/args/lib/args.dart

Index: pkg/args/lib/args.dart
diff --git a/pkg/args/lib/args.dart b/pkg/args/lib/args.dart
index 7f524dfb4268125f893ac7374410269875eeab95..a76e72646d8afffa488f268200258c3139bba516 100644
--- a/pkg/args/lib/args.dart
+++ b/pkg/args/lib/args.dart
@@ -321,9 +321,9 @@ class ArgParser {
    * * There is already an option using abbreviation [abbr].
    */
   void addFlag(String name, {String abbr, String help, bool defaultsTo: false,
-      bool negatable: true, void callback(bool value)}) {
+      bool negatable: true, void callback(bool value), bool hide: false}) {
     _addOption(name, abbr, help, null, null, defaultsTo, callback,
-        isFlag: true, negatable: negatable);
+        isFlag: true, negatable: negatable, hide: hide);
   }
 
   /**