Add whitelist support for grit repack steps.

build/repack_action.gypi

 # Copyright 2014 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.
 
 # This file is meant to be included into an action to invoke grit repack in a
 # consistent manner. To use this the following variables need to be
 # defined:
 #   pak_inputs: list: paths of pak files that need to be combined.
 #   pak_output: string: the output pak file path. 
 
 {
   'variables': {
     'repack_path': '<(DEPTH)/tools/grit/grit/format/repack.py',
+    'repack_options%': [],
   },
   'inputs': [
     '<(repack_path)',
     '<@(pak_inputs)',
   ],
   'outputs': [
     '<(pak_output)'
   ],
-  'action': ['python', '<(repack_path)', '<(pak_output)', '<@(pak_inputs)'],
+  'action': [
+    'python',
+    '<(repack_path)',
+    '<@(repack_options)',
+    '<(pak_output)',
+    '<@(pak_inputs)',
+  ],
 }