Change how MB handles goma_dir.

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 1670 matching lines @@
       # actually work, so we need to pretend to be doing an ozone build
       # in order for the flag to actually take effect.
       'gn_args': 'use_ozone=true',
     },
 
     'gn': {'type': 'gn'},
 
     'goma': {
       # The MB code will properly escape goma_dir if necessary in the GYP
       # code path; the GN code path needs no escaping.
-      'gn_args': 'use_goma=true goma_dir="$(goma_dir)"',
-      'gyp_defines': 'use_goma=1 gomadir=$(goma_dir)',
+      'gn_args': 'use_goma=true',
+      'gyp_defines': 'use_goma=1',
     },
 
     'gpu_tests': {
       'mixins': ['archive_gpu_tests', 'chrome_with_codecs'],
     },
 
     'gyp': {'type': 'gyp'},
 
     'internal_gles2_conform_tests': {
       'gn_args': 'internal_gles2_conform_tests=true',
@@ skipping 130 matching lines @@
       'gn_args': 'is_component_build=true enable_iterator_debugging=false',
       'gyp_defines': 'component=shared_library build_for_tool=drmemory',
     },
 
     'valgrind': {
       # TODO: add gn_args for 'build_for_tool=memcheck'
       'gyp_defines': 'build_for_tool=memcheck',
     }
   },
 }