Add try server configuration for 'git cl try'.

PRESUBMIT.py

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 80 matching lines @@
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(_CheckChangeLogFlag(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   if not _SkipTreeCheck(input_api, output_api):
     results.extend(input_api.canned_checks.CheckTreeIsOpen(
         input_api, output_api,
         json_url='http://v8-status.appspot.com/current?format=json'))
   return results
+
+
+def GetPreferredTryMasters(project, change):
+  return {
+    'tryserver.v8': {
+      'v8_mac_rel': set(['defaulttests']),
+      'v8_win_rel': set(['defaulttests']),
+    },
+  }