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

ui/events/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/ui/events
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details on the presubmit API built into gcl.
 """
 
-def GetPreferredTrySlaves():
+def GetPreferredTryMasters(project, change):
   tests = set(['ash_unittests',
                'aura_unittests',
                'events_unittests',
                'keyboard_unittests',
                'views_unittests'])
 
-  return [('linux_rel', tests),
-          ('linux_chromeos', tests),
-          ('linux_chromeos_asan', tests),
-          ('win', tests),
-          ('win_rel', tests)]
+  return {
+    'tryserver.chromium': {
+      'linux_rel': tests,
+      'linux_chromeos': tests,
+      'linux_chromeos_asan': tests,
+      'win': tests,
+      'win_rel': tests,
+    }
+  }