Convert most Chromium presubmit files to use new multiple-tryserver-compatible protocol

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 30 matching lines @@
   results.extend(_CommonChecks(input_api, output_api))
   return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   return results
 
 
-def GetPreferredTrySlaves():
-  return [
-    'linux_rel:sync_integration_tests',
-    'mac_rel:sync_integration_tests',
-    'win_rel:sync_integration_tests',
-  ]
+def GetPreferredTryMasters(project, change):
+  return {
+    'tryserver.chromium': {
+      'linux_rel': set(['sync_integration_tests']),
+      'mac_rel': set(['sync_integration_tests']),
+      'win_rel': set(['sync_integration_tests']),
+    }
+  }