Change core lib, dart2js, and more for new optional parameters syntax

pkg/args/lib/args.dart

Index: pkg/args/lib/args.dart
===================================================================
--- pkg/args/lib/args.dart	(revision 13588)
+++ pkg/args/lib/args.dart	(working copy)
@@ -560,8 +560,8 @@
   final bool allowMultiple;
 
   _Option(this.name, this.abbreviation, this.help, this.allowed,
-      this.allowedHelp, this.defaultValue, this.callback, [this.isFlag,
-      this.negatable, this.allowMultiple = false]);
+      this.allowedHelp, this.defaultValue, this.callback, {this.isFlag,
+      this.negatable, this.allowMultiple: false});
 }
 
 /**