Enable post-compile test isolation for all CI builders.

scripts/slave/recipe_modules/chromium/chromium_linux.py

 # 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.
 
 from . import steps
 
 SPEC = {
   'settings': {
     'build_gs_bucket': 'chromium-linux-archive',
   },
   'builders': {
     'Linux Builder': {
       'recipe_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Release',
         'TARGET_BITS': 64,
       },
       'bot_type': 'builder',
       'compile_targets': [
         'chromium_swarm_tests',
       ],
       'testing': {
         'platform': 'linux',
       },
       'use_isolate': True,
       'enable_swarming': True,
-      'isolation_mode': 'prepare',
     },
     'Linux Tests': {
       'recipe_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Release',
         'TARGET_BITS': 64,
       },
       'bot_type': 'tester',
       'test_generators': [
         steps.generate_gtest,
@@ skipping 187 matching lines @@
             test_data='content:content/test/data/android/device_files',
             adb_install_apk=(
                 'ContentShell.apk', 'org.chromium.content_shell_apk')),
       ],
       'testing': {
         'platform': 'linux',
       },
     },
   },
 }