Change grit whitelist to a string parameter

ios/chrome/ios_chrome_resources.gyp

 # Copyright 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': {
     'chromium_code': 1,
     'grit_base_dir': '<(SHARED_INTERMEDIATE_DIR)',
     'grit_out_dir': '<(grit_base_dir)/ios/chrome',
-    'grit_defines': [
-      # TODO(lliabraa): Remove this whitelist.
-      '-w', '<(DEPTH)/ios/build/grit_whitelist.txt',
-    ],
+    # TODO(lliabraa): Remove this whitelist.
+    'grit_whitelist': '<(DEPTH)/ios/build/grit_whitelist.txt',
   },
   'targets': [
     {
       'target_name': 'ios_theme_resources_gen',
       'type': 'none',
       'actions': [
         {
           'action_name': 'ios_theme_resources',
           'variables': {
             'grit_grd_file': 'app/theme/ios_theme_resources.grd',
           },
           'includes': [ '../../build/grit_action.gypi' ],
         },
       ],
       'includes': [ '../../build/grit_target.gypi' ],
       # Override the exported include-dirs; ios_theme_resources.h should only be
       # referencable as ios/chrome/grit/, to allow DEPS-time checking of usage.
       'direct_dependent_settings': {
         'include_dirs': [
           '<(grit_base_dir)',
         ],
         'include_dirs!': [
           '<(grit_out_dir)',
         ],
       },
     },
   ],
 }