Add support for cros chrome_sdk (simplechrome) to MB.

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 map of buildbot master names -> buildbot builder names ->
   # config names (where each config name is a key in the 'configs' dict,
   # below). MB uses this dict to look up which config to use for a given bot.
   'masters': {
     # Take care when changing any of these builders to ensure that you do not
@@ skipping 1030 matching lines @@
     ],
 
     'chromeos_ozone_gn_release_trybot': [
       'chromeos', 'ozone', 'gn', 'release_trybot',
     ],
 
     # The 'cros_chrome_sdk_* configs are placeholders that indicate
     # that the GYP_DEFINES (or GN args) are set by the `cros chrome-sdk`
     # wrapper and need to be looked at specially.
     'cros_chrome_sdk_gyp': [
-      'gyp', 'error',
+      'gyp', 'cros_chrome_sdk',
     ],
 
     # The 'findit' config is used by the *_variable_* bots, which run
     # the 'FindIt' recipes and code to bisect failures that happen on the
     # other waterfall bots. The findit recipes actually override and
     # re-use the configs from the matching waterfall bots, and so it should
     # be an error if MB ever sees an actual *_variable_* bot name.
     'findit': [
       'error',
     ],
@@ skipping 842 matching lines @@
 
     'cronet': {
       'gn_args': ('disable_file_support=true disable_ftp_support=true '
                   'enable_websockets=false use_platform_icu_alternatives=true '
                   'disable_brotli_filter=true'),
       'gyp_defines': ('disable_file_support=1 disable_ftp_support=1 '
                       'enable_websockets=0 use_platform_icu_alternatives=1 '
                       'disable_brotli_filter=1'),
     },
 
+    'cros_chrome_sdk': {
+      # This is used so that the cros chrome_sdk (simplechrome) builders
+      # can manage the list of GYP_DEFINES and gn args in their .ebuild
+      # files and just pass through the desired arguments, hence not
+      # really using MB. If a bot uses this mixin, we expect that
+      # both GYP_DEFINES and GN_ARGS are set in the environment,
+      # and that GYP_DEFINES has chromeos=1 and GN_ARGS has
+      # target_os="chromeos" in it.
+      'cros_passthrough': True,
+    },
+
     'crosscompile': {
       # This mixin is only needed on GYP bots that are doing cross-compiles
       # but are *not* targetting Android or iOS (where build/gyp_chromium
       # will set the crosscompile variable automatically). It is not need
       # in GN at all.
       'gyp_crosscompile': True,
     },
 
     'data_reduction_proxy': {
       'gn_args': 'cronet_enable_data_reduction_proxy_support=true',
@@ skipping 290 matching lines @@
     },
 
     'drfuzz': { 'gn_args': 'use_drfuzz=true' },
 
     'drmemory': {
       'gn_args': 'is_component_build=true enable_iterator_debugging=false',
       'gyp_defines': 'component=shared_library build_for_tool=drmemory',
     },
   },
 }