Add PRESUBMIT check if modified UMA histogram name can be found

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 328 matching lines @@
              '=======',
              '  ScopedTempDir temp_dir_;',
              '>>>>>>> master']
     errors = PRESUBMIT._CheckForVersionControlConflictsInFile(
         MockInputApi(), MockFile('some/path/foo_platform.cc', lines))
     self.assertEqual(3, len(errors))
     self.assertTrue('1' in errors[0])
     self.assertTrue('3' in errors[1])
     self.assertTrue('5' in errors[2])
 
+class UmaHistogramChangeMatchedOrNotTest(unittest.TestCase):
+  def testTypicalNotMatchedChange(self):
+    diff = ['UMA_HISTOGRAM_BOOL("Bla.Foo.Dummy", true)']
+    mock_input_api = MockInputApi()
+    mock_input_api.files = [MockFile('some/path/foo.cc', diff)]
+    warnings = PRESUBMIT._CheckUmaHistogramChanges(mock_input_api,
+                                                   MockOutputApi())
+    self.assertEqual(1, len(warnings))
+    self.assertEqual('warning', warnings[0].type)
+
+  def testTypicalCorrectlyMatchedChange(self):
+    diff_cc = ['UMA_HISTOGRAM_BOOL("Bla.Foo.Dummy", true)']
+    diff_xml = ['<histogram name="Bla.Foo.Dummy"> </histogram>']
+    mock_input_api = MockInputApi()
+    mock_input_api.files = [
+      MockFile('some/path/foo.cc', diff_cc),
+      MockFile('tools/metrics/histograms/histograms.xml', diff_xml),
+    ]
+    warnings = []
+    warnings = PRESUBMIT._CheckUmaHistogramChanges(mock_input_api,
+                                                   MockOutputApi())
+    self.assertEqual(0, len(warnings))
 
 class BadExtensionsTest(unittest.TestCase):
   def testBadRejFile(self):
     mock_input_api = MockInputApi()
     mock_input_api.files = [
       MockFile('some/path/foo.cc', ''),
       MockFile('some/path/foo.cc.rej', ''),
       MockFile('some/path2/bar.h.rej', ''),
     ]
 
@@ skipping 409 matching lines @@
     }
     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)))
 
 
 if __name__ == '__main__':
   unittest.main()