Add PRESUBMIT check if modified UMA histogram name can be found

PRESUBMIT_test.py

Index: PRESUBMIT_test.py
diff --git a/PRESUBMIT_test.py b/PRESUBMIT_test.py
index 2f377084548507fa30d8de02ced24d803ef2e94d..1c97191755654d17440de816a3debdeb2d6ebf10 100755
--- a/PRESUBMIT_test.py
+++ b/PRESUBMIT_test.py
@@ -346,6 +346,28 @@ class VersionControlConflictsTest(unittest.TestCase):
     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):