add verbose option to show hidden args

pkg/dev_compiler/lib/src/compiler/module_builder.dart

 // Copyright (c) 2015, 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.
 
 import 'package:args/args.dart' show ArgParser, ArgResults;
 import 'package:path/path.dart' as path;
 
 import '../js_ast/js_ast.dart';
 import 'js_names.dart';
 
@@ skipping 27 matching lines @@
   var format = argResults['modules'];
   if (format is String) {
     return [parseModuleFormat(format)];
   }
   return (format as List<String>).map(parseModuleFormat).toList();
 }
 
 /// Adds an option to the [argParser] for choosing the module format, optionally
 /// [allowMultiple] formats to be specified, with each emitted into a separate
 /// file.
-void addModuleFormatOptions(ArgParser argParser, {bool allowMultiple: false}) {
+void addModuleFormatOptions(ArgParser argParser,
+    {bool allowMultiple: false, bool hide: true}) {
   argParser
     ..addOption('modules',
         help: 'module pattern to emit',
         allowed: [
           'es6',
           'common',
           'amd',
           'legacy', // deprecated
           'node', // renamed to commonjs
           'all' // to emit all flavors for the SDK
         ],
         allowedHelp: {
           'es6': 'ECMAScript 6 modules',
           'common': 'CommonJS/Node.js modules',
           'amd': 'AMD/RequireJS modules'
         },
         allowMultiple: allowMultiple,
         defaultsTo: 'amd')
     ..addFlag('single-out-file',
         help: 'emit modules that can be concatenated into one file.\n'
             'Only compatible with legacy and amd module formats.',
         defaultsTo: false,
-        hide: true);
+        hide: hide);
 }
 
 /// Transforms an ES6 [module] into a given module [format].
 ///
 /// If the format is [ModuleFormat.es6] this will return [module] unchanged.
 ///
 /// Because JS ASTs are immutable the resulting module will share as much
 /// structure as possible with the original. The transformation is a shallow one
 /// that affects the top-level module items, especially [ImportDeclaration]s and
 /// [ExportDeclaration]s.
@@ skipping 251 matching lines @@
   // Ensure the identifier first character is not numeric and that the whole
   // identifier is not a keyword.
   if (result.startsWith(new RegExp('[0-9]')) || invalidVariableName(result)) {
     return '\$$result';
   }
   return result;
 }
 
 // Invalid characters for identifiers, which would need to be escaped.
 final _invalidCharInIdentifier = new RegExp(r'[^A-Za-z_$0-9]');