Add PRESUBMIT tests for _CheckUserActionUpdate function.

PRESUBMIT_test.py

Index: PRESUBMIT_test.py
diff --git a/PRESUBMIT_test.py b/PRESUBMIT_test.py
index ad391d3cbcfe49dcc0f4114b122fda03842f50c5..8b642c4efb5039f3c7972a40c5b9dbe680249d56 100755
--- a/PRESUBMIT_test.py
+++ b/PRESUBMIT_test.py
@@ -775,5 +775,39 @@ class TryServerMasterTest(unittest.TestCase):
             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()