Update manually triggered try jobs to use swarming for ChromeOS and Mac since they're switched by C…

base/PRESUBMIT.py

 # 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.
 
 """Chromium presubmit script for src/base.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details on the presubmit API built into gcl.
 """
 
@@ skipping 36 matching lines @@
   results.extend(_CommonChecks(input_api, output_api))
   return results
 
 
 def GetPreferredTryMasters(project, change):
   return {
     'tryserver.chromium.linux': {
       'linux_chromium_rel_swarming': set(['defaulttests']),
     },
     'tryserver.chromium.mac': {
-      'mac_chromium_rel': set(['defaulttests']),
+      'mac_chromium_rel_swarming': set(['defaulttests']),
     },
     'tryserver.chromium.win': {
       'win_chromium_rel': set(['defaulttests']),
     }
   }