More sync of PRESUBMIT with what CQ runs

chrome/browser/extensions/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/chrome/browser/extensions.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details on the presubmit API built into gcl.
 """
 
 def GetPreferredTryMasters(project, change):
   return {
     'tryserver.chromium': {
-      'linux_chromeos': set(['defaulttests']),
+      'linux_chromium_chromeos_rel': set(['defaulttests']),
     }
   }
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results += input_api.canned_checks.CheckPatchFormatted(input_api, output_api)
   return results