Make swarming dimensions for GPU bots explicit

scripts/slave/recipe_modules/chromium_tests/chromium_gpu.py

 # 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.
 
 from . import steps
 
 SPEC = {
   'settings': {
     'build_gs_bucket': 'chromium-gpu-archive',
     # WARNING: src-side runtest.py is only tested with chromium CQ builders.
@@ skipping 262 matching lines @@
         steps.generate_gtest,
         steps.generate_script,
         steps.generate_isolated_script,
       ],
       'bot_type': 'tester',
       'parent_buildername': 'GPU Mac Builder (dbg)',
       'testing': {
         'platform': 'mac',
       },
       'enable_swarming': True,
+      'swarming_dimensions': {
+        'os': 'Mac-10.10',
+      },
     },
     'Mac Retina Release': {
       'chromium_config': 'chromium',
       'chromium_apply_config': ['ninja_confirm_noop'],
       'gclient_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Release',
         'TARGET_BITS': 64,
       },
       'test_generators': [
@@ skipping 40 matching lines @@
         steps.generate_gtest,
         steps.generate_script,
         steps.generate_isolated_script,
       ],
       'bot_type': 'tester',
       'parent_buildername': 'GPU Mac Builder',
       'testing': {
         'platform': 'mac',
       },
       'enable_swarming': True,
+      'swarming_dimensions': {
+        'os': 'Mac-10.10',
+      },
     },
     'Mac 10.10 Retina Debug (AMD)': {
       'chromium_config': 'chromium',
       'chromium_apply_config': ['ninja_confirm_noop'],
       'gclient_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Debug',
         'TARGET_BITS': 64,
       },
       'test_generators': [
         steps.generate_gtest,
         steps.generate_script,
         steps.generate_isolated_script,
       ],
       'bot_type': 'tester',
       'parent_buildername': 'GPU Mac Builder (dbg)',
       'testing': {
         'platform': 'mac',
       },
       'enable_swarming': True,
+      'swarming_dimensions': {
+        'os': 'Mac-10.10',
+      },
     },
   },
 }