Use Xvfb in isolated testing only if use_x11 is set (reland)

build/isolate.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.
 
 # This file is meant to be included into a target to provide a rule
 # to "build" .isolate files into a .isolated file.
 #
 # To use this, create a gyp target with the following form:
 # 'conditions': [
 #   ['test_isolation_mode != "noop"', {
@@ skipping 77 matching lines @@
           'internal_gles2_conform_tests=<(internal_gles2_conform_tests)',
         '--config-variable', 'libpeer_target_type=<(libpeer_target_type)',
         '--config-variable', 'lsan=<(lsan)',
         '--config-variable', 'msan=<(msan)',
         '--config-variable', 'target_arch=<(target_arch)',
         '--config-variable', 'tsan=<(tsan)',
         '--config-variable', 'use_custom_libcxx=<(use_custom_libcxx)',
         '--config-variable', 'use_instrumented_libraries=<(use_instrumented_libraries)',
         '--config-variable', 'use_openssl=<(use_openssl)',
         '--config-variable', 'use_ozone=<(use_ozone)',
+        '--config-variable', 'use_x11=<(use_x11)',
         '--config-variable', 'v8_use_external_startup_data=<(v8_use_external_startup_data)',
       ],
       'conditions': [
         # Note: When gyp merges lists, it appends them to the old value.
         ['OS=="mac"', {
           # <(mac_product_name) can contain a space, so don't use FOO=<(FOO)
           # form.
           'action': [
             '--extra-variable', 'mac_product_name', '<(mac_product_name)',
           ],
         }],
         ["test_isolation_outdir!=''", {
           'action': [ '--isolate-server', '<(test_isolation_outdir)' ],
         }],
         ["test_isolation_mode == 'prepare'", {
           'outputs': [
             '<(PRODUCT_DIR)/<(RULE_INPUT_ROOT).isolated.gen.json',
           ],
         }, {
           'outputs': [
             '<(PRODUCT_DIR)/<(RULE_INPUT_ROOT).isolated',
           ],
         }],
       ],
     },
   ],
 }