Have iOS use the same atomicops_internal implementation that Mac uses.

base/base.gypi

 # 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 30 matching lines @@
           'android/jni_string.h',
           'android/locale_utils.cc',
           'android/locale_utils.h',
           'android/path_utils.cc',
           'android/path_utils.h',
           'at_exit.cc',
           'at_exit.h',
           'atomic_ref_count.h',
           'atomic_sequence_num.h',
           'atomicops.h',
+          'atomicops_internals_mac.h',
           'atomicops_internals_x86_gcc.cc',
           'atomicops_internals_x86_gcc.h',
           'atomicops_internals_x86_msvc.h',
           'base_export.h',
           'base_paths.cc',
           'base_paths.h',
           'base_paths_android.cc',
           'base_paths_android.h',
           'base_paths_mac.h',
           'base_paths_mac.mm',
@@ skipping 491 matching lines @@
               ['include', '^process_util_linux\\.cc$'],
               ['include', '^sys_info_linux\\.cc$'],
               ['include', '^sys_string_conversions_posix\\.cc$'],
               ['include', '^worker_pool_linux\\.cc$'],
             ],
           }],
           ['OS == "ios"', {
             'sources/': [
               # Pull in specific Mac files for iOS (which have been filtered out
               # by file name rules).
+              ['include', '^atomicops_internals_mac\\.'],
               ['include', '^base_paths_mac\\.'],
               ['include', '^file_util_mac\\.'],
               ['include', '^file_version_info_mac\\.'],
               ['include', '^mac/bundle_locations\\.'],
               ['include', '^mac/foundation_util\\.'],
               ['include', '^mac/mac_logging\\.'],
               ['include', '^mac/objc_property_releaser\\.'],
               ['include', '^mac/scoped_nsautorelease_pool\\.'],
               ['include', '^message_pump_mac\\.'],
               ['include', '^native_library_mac\\.'],
@@ skipping 75 matching lines @@
           ['<(chromeos)!=1 or >(nacl_untrusted_build)==1', {
             'sources/': [
               ['exclude', '^chromeos/'],
             ],
           }],
         ],
       }],
     ],
   },
 }