Add build rules for dart2js.

dart/dart.gyp

-# Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+# Copyright (c) 2012, 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.
 
 {
   'variables': {
     # These variables are used in the creation of the .vcproj file on 
     # Windows.
     'cygwin_dir': 'third_party/cygwin',
   },
   'targets': [
@@ skipping 86 matching lines @@
           'outputs': [
             '<(PRODUCT_DIR)/upload_sdk',
           ],
           'action': [
             'python',
             'tools/upload_sdk.py',
             '<(PRODUCT_DIR)/dart-sdk'
           ],
         },
       ],
-    }
+    },
+    {
+      'target_name': 'dart2js',
+      'type': 'none',
+      'dependencies': [
+        'runtime/dart-runtime.gyp:dart',
+        'utils/compiler/compiler.gyp:dart2js',
+      ],
+    },
   ],
 }