GN: get echo-headers sources via exec_script

gyp/harfbuzz.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'hb_directory': '../third_party/externals/harfbuzz',
   },
   'targets': [
     {
       'target_name': 'harfbuzz',
       'type': 'static_library',
       'defines': [
         'HAVE_OT',
         'HAVE_ICU',
         'HAVE_ICU_BUILTIN',
         'HB_NO_MT',
       ],
       'sources': [
-        '<!@(python find.py <(hb_directory)/src "hb-*.c*")',
+        '<!@(python find.py "hb-*.c*" <(hb_directory)/src)',
       ],
       'sources!': [
         '<(hb_directory)/src/hb-directwrite.cc',
         '<(hb_directory)/src/hb-ft.cc',
         '<(hb_directory)/src/hb-glib.cc',
         '<(hb_directory)/src/hb-gobject-structs.cc',
         '<(hb_directory)/src/hb-graphite2.cc',
         '<(hb_directory)/src/hb-ucdn.cc',
         '<(hb_directory)/src/hb-uniscribe.cc',
       ],
@@ skipping 21 matching lines @@
           {
             'defines': [ 'HAVE_CORETEXT', ],
           }, {
             'sources!': [ '<(hb_directory)/src/hb-coretext.cc', ],
           }
         ],
       ],
     },
   ],
 }