Add --modules=node support

lib/src/options.dart

 // Copyright (c) 2014, 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.
 
 /// Set of flags and options passed to the compiler
 library dev_compiler.src.options;
 
 import 'dart:io';
 
 import 'package:args/args.dart';
@@ skipping 40 matching lines @@
       {this.useMockSdk: false,
       this.dartSdkPath,
       this.useMultiPackage: false,
       this.customUrlMappings: const {},
       this.packageRoot: 'packages/',
       this.packagePaths: const <String>[],
       this.resources: const <String>[],
       this.useImplicitHtml: false});
 }
 
-enum ModuleFormat { es6, legacy }
+enum ModuleFormat { es6, legacy, node }
 ModuleFormat parseModuleFormat(String s) => parseEnum(s, ModuleFormat.values);
 
 // TODO(jmesserly): refactor all codegen options here.
 class CodegenOptions {
   /// Whether to emit the source map files.
   final bool emitSourceMaps;
 
   /// Whether to force compilation of code with static errors.
   final bool forceCompile;
 
@@ skipping 236 matching lines @@
   ..addOption('runtime-dir',
       help: 'Where to find dev_compiler\'s runtime files', defaultsTo: null)
   ..addFlag('arrow-fn-bind-this',
       help: 'Work around `this` binding in => functions')
   ..addOption('modules',
       help: 'Which module pattern to emit',
       allowed: ModuleFormat.values.map(getEnumName).toList(),
       allowedHelp: {
         getEnumName(ModuleFormat.es6): 'es6 modules',
         getEnumName(ModuleFormat.legacy):
-            'a custom format used by dartdevc, similar to AMD'
+            'a custom format used by dartdevc, similar to AMD',
+        getEnumName(ModuleFormat.node):
+            'node.js modules (https://nodejs.org/api/modules.html)'
       },
       defaultsTo: getEnumName(ModuleFormat.legacy))
 
   // general options
   ..addFlag('help', abbr: 'h', help: 'Display this message')
   ..addFlag('version',
       negatable: false, help: 'Display the Dev Compiler verion')
   ..addFlag('server', help: 'Run as a development server.', defaultsTo: false)
   ..addFlag('hashing',
       help: 'Enable hash-based file caching.', defaultsTo: null)
@@ skipping 80 matching lines @@
     // The pub-cache directory is two levels up, but we verify that the layout
     // looks correct.
     if (path.basename(dir) != 'dev_compiler') return null;
     dir = path.dirname(dir);
     if (path.basename(dir) != 'global_packages') return null;
     dir = path.dirname(dir);
     return path.join(dir, cacheDir, 'lib', 'runtime');
   }
   return null;
 }