Run Ozone CrOS tests with X11 platform by default.

tools/mb/mb_config.pyl

 # 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.
 
 # This is a .pyl, or "Python Literal", file. You can treat it just like a
 # .json file, with the following exceptions:
 # * all keys must be quoted (use single quotes, please);
 # * comments are allowed, using '#' syntax; and
 # * trailing commas are allowed.
 
@@ skipping 1014 matching lines @@
 
     'chromeos_with_codecs_debug_bot': [
       'chromeos_with_codecs', 'debug_bot',
     ],
 
     'chromeos_with_codecs_debug_trybot': [
       'chromeos_with_codecs', 'debug_trybot',
     ],
 
     'chromeos_with_codecs_ozone_release_bot': [
-      'chromeos_with_codecs', 'ozone', 'release_bot',
+      'chromeos_with_codecs', 'ozone', 'default_ozone_platform_x11', 'release_bot',
     ],
 
     'chromeos_with_codecs_ozone_release_trybot': [
-      'chromeos_with_codecs', 'ozone', 'release_trybot',
+      'chromeos_with_codecs', 'ozone', 'default_ozone_platform_x11', 'release_trybot',
     ],
 
     'chromeos_with_codecs_release_bot': [
       'chromeos_with_codecs', 'release_bot',
     ],
 
     'chromeos_with_codecs_release_trybot': [
       'chromeos_with_codecs', 'release_trybot',
     ],
 
@@ skipping 591 matching lines @@
     },
 
     'debug_static_bot': {
       'mixins': ['debug', 'static', 'minimal_symbols', 'goma'],
     },
 
     'debug_trybot': {
       'mixins': ['debug_bot', 'minimal_symbols'],
     },
 
+    'default_ozone_platform_x11': {
+      'gn_args': 'ozone_platform="x11"',
+    },
+
     'disable_nacl': {
       'gn_args': 'enable_nacl=false',
     },
 
     'edge': {
       'gn_args': 'sanitizer_coverage_flags="edge"',
     },
 
     # This mixin is used to force configs that use it to fail. It
     # is used in two cases: when we have bots that we haven't looked
@@ skipping 221 matching lines @@
 
     'x64': {
       'gn_args': 'target_cpu="x64"',
     },
 
     'x86': {
       'gn_args': 'target_cpu="x86"',
     },
   },
 }