Add PRESUBMIT tests for _CheckUserActionUpdate function.

PRESUBMIT_test.py

 #!/usr/bin/env python
 # 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.
 
 import glob
 import json
 import os
 import re
 import subprocess
@@ skipping 757 matching lines @@
             'win_rel_naclmore',
          ],
     }
     for master, bots in bots.iteritems():
       for bot in bots:
         self.assertEqual(master, PRESUBMIT.GetTryServerMasterForBot(bot),
                          'bot=%s: expected %s, computed %s' % (
             bot, master, PRESUBMIT.GetTryServerMasterForBot(bot)))
 
 
+class UserMetricsActionTest(unittest.TestCase):
+  def testUserMetricsActionInActions(self):
+    input_api = MockInputApi()
+    file_with_user_action = 'file_with_user_action.cc'
+    contents_with_user_action = [
+      'base::UserMetricsAction("AboutChrome")'
+    ]
+
+    input_api.files = [MockFile(file_with_user_action,
+                                contents_with_user_action)]
+
+    self.assertEqual(
+      [], PRESUBMIT._CheckUserActionUpdate(input_api, MockOutputApi()))
+
+
+  def testUserMetricsActionNotAddedToActions(self):
+    input_api = MockInputApi()
+    file_with_user_action = 'file_with_user_action.cc'
+    contents_with_user_action = [
+      'base::UserMetricsAction("NotInActionsXml")'
+    ]
+
+    input_api.files = [MockFile(file_with_user_action,
+                                contents_with_user_action)]
+
+    output = PRESUBMIT._CheckUserActionUpdate(input_api, MockOutputApi())
+    self.assertEqual(
+      ('File %s line %d: %s is missing in '
+       'tools/metrics/actions/actions.xml. Please run '
+       'tools/metrics/actions/extract_actions.py to update.'
+       % (file_with_user_action, 1, 'NotInActionsXml')),
+      output[0].message)
+
+
 if __name__ == '__main__':
   unittest.main()