V8: Fix preferred builder setup

masters/master.tryserver.v8/master.cfg

 #!/usr/bin/env python
 # Copyright 2013 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.
 
 import os
 
 from common import chromium_utils
 
 from master import master_utils
@@ skipping 241 matching lines @@
 
 slaves = slaves_list.SlavesList('slaves.cfg', 'V8TryServer')
 for builder in c['builders']:
   # Associate the slaves to the builders. The configuration is in slaves.cfg.
   builder['slavenames'] = slaves.GetSlavesName(builder=builder['name'])
   # Sets nextSlave function for slave affinity.
   builder['nextSlave'] = master_utils.PreferredBuilderNextSlaveFuncNG()
 
 # The 'slaves' list defines the set of allowable buildslaves. List all the
 # slaves registered to a builder. Remove dupes.
-c['slaves'] = master_utils.AutoSetupSlaves(c['builders'],
-                                           config.Master.GetBotPassword())
+c['slaves'] = master_utils.AutoSetupSlaves(
+    c['builders'],
+    config.Master.GetBotPassword(),
+    preferred_builder_dict=slaves.GetPreferredBuildersDict())
 
 # Make sure everything works together.
 master_utils.VerifySetup(c, slaves)
 
 ####### STATUS TARGETS
 
 # Buildbot master url:
 # Must come before AutoSetupMaster().
 c['buildbotURL'] = ActiveMaster.buildbot_url
 
@@ skipping 29 matching lines @@
 c['logHorizon'] = 2000
 # Must be at least 2x the number of slaves.
 c['eventHorizon'] = 200
 # Adjust the buildCaches to be 3x the number of slaves per builder.
 c['autoBuildCacheRatio'] = 3
 
 ####### PROJECT IDENTITY
 
 c['projectName'] = ActiveMaster.project_name
 c['projectURL'] = config.Master.project_url