Download the hermetic xcode toolchain on all bots that target mac.

scripts/slave/recipe_modules/chromium_tests/chromium_gpu.py

 # Copyright 2015 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.
 
 from . import steps
 
 SPEC = {
   'settings': {
     'build_gs_bucket': 'chromium-gpu-archive',
     # WARNING: src-side runtest.py is only tested with chromium CQ builders.
@@ skipping 152 matching lines @@
       },
       'enable_swarming': True,
     },
     'GPU Mac Builder': {
       'chromium_config': 'chromium',
       'chromium_apply_config': [
         'archive_gpu_tests',
         'chrome_with_codecs',
         'mb',
         'ninja_confirm_noop',
-        'force_mac_toolchain',
       ],
       'gclient_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Release',
         'TARGET_BITS': 64,
       },
       'bot_type': 'builder',
       'compile_targets': [
       ],
       'testing': {
         'platform': 'mac',
       },
       'enable_swarming': True,
       'use_isolate': True,
       'checkout_dir': 'mac',
     },
     'GPU Mac Builder (dbg)': {
       'chromium_config': 'chromium',
       'chromium_apply_config': [
         'archive_gpu_tests',
         'chrome_with_codecs',
         'mb',
         'ninja_confirm_noop',
-        'force_mac_toolchain',
       ],
       'gclient_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Debug',
         'TARGET_BITS': 64,
       },
       'bot_type': 'builder',
       'compile_targets': [
       ],
       'testing': {
@@ skipping 57 matching lines @@
       },
       'bot_type': 'tester',
       'parent_buildername': 'GPU Mac Builder (dbg)',
       'testing': {
         'platform': 'mac',
       },
       'enable_swarming': True,
     },
   },
 }