Only list dart files in pkg files dependency

pkg/pkg_files.gyp

 # 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.
 
 {
   'targets': [
     # Other targets depend on pkg files, but have to many inputs, which causes
     # issues on some platforms.
     # This target lists all the files in pkg and third_party/pkg,
     # and creates a single pkg_files.stamp
     {
       'target_name': 'pkg_files_stamp',
       'type': 'none',
       'actions': [
         {
           'action_name': 'make_pkg_files_stamp',
           'inputs': [
             '../tools/create_timestamp_file.py',
-            '<!@(["python", "../tools/list_files.py", "", "."])',
-            '<!@(["python", "../tools/list_files.py", "",'
+            '<!@(["python", "../tools/list_files.py", "\\.dart$", "."])',
+            '<!@(["python", "../tools/list_files.py", "\\.dart$",'
                 '"../third_party/pkg"])',
           ],
           'outputs': [
             '<(SHARED_INTERMEDIATE_DIR)/pkg_files.stamp',
           ],
           'action': [
             'python', '../tools/create_timestamp_file.py',
             '<@(_outputs)',
           ],
         },
       ],
     }
   ],
 }