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

extensions/browser/PRESUBMIT.py

 # Copyright 2014 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/extensions/browser.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details on the presubmit API built into gcl.
 """
 
-def GetPreferredTrySlaves():
-  return ['linux_chromeos']
+def GetPreferredTryMasters(project, change):
+  return {
+    'tryserver.chromium': {
+      'linux_chromeos': set(['defaulttests']),
+    }
+  }
 
 class HistogramValueChecker(object):
   """Verify that changes to "extension_function_histogram_value.h" are valid.
 
   See comments at the top of the "extension_function_histogram_value.h" file
   for what are considered valid changes. There are situations where this script
   gives false positive warnings, i.e. it warns even though the edit is
   legitimate. Since the script warns using prompt warnings, the user can always
   choose to continue. The main point is to attract the attention to all
   (potentially or not) invalid edits.
@@ skipping 272 matching lines @@
       if file.LocalPath() == self.LOCAL_PATH:
         self.ProcessHistogramValueFile(file)
     return self.results
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results += HistogramValueChecker(input_api, output_api).Run()
   results += input_api.canned_checks.CheckPatchFormatted(input_api, output_api)
   return results