gpu: Add linux optional GPU tests to presubmit.

gpu/PRESUBMIT.py

 # Copyright (c) 2016 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.
 
 """Top-level presubmit script for gpu.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
 import re
 
 def PostUploadHook(cl, change, output_api):
   """git cl upload will call this hook after the issue is created/modified.
 
   This hook adds extra try bots list to the CL description in order to run
   Blink tests in addition to CQ try bots.
   """
   rietveld_obj = cl.RpcServer()
   issue = cl.issue
   description = rietveld_obj.get_description(issue)
   if re.search(r'^CQ_INCLUDE_TRYBOTS=.*', description, re.M | re.I):
     return []
 
   bots = [
+    'tryserver.chromium.linux:linux_optional_gpu_tests_rel',
+    'tryserver.chromium.mac:mac_optional_gpu_tests_rel',
     'tryserver.chromium.win:win_optional_gpu_tests_rel',
-    'tryserver.chromium.mac:mac_optional_gpu_tests_rel',
   ]
 
   results = []
   new_description = description
   new_description += '\nCQ_INCLUDE_TRYBOTS=%s' % ';'.join(bots)
   results.append(output_api.PresubmitNotifyResult(
       'Automatically added optional GPU tests to run on CQ.'))
 
   if new_description != description:
     rietveld_obj.update_description(issue, new_description)
 
   return results