Add a presubmit checker for duplicated enum values in UseCounter::Feature

third_party/WebKit/Source/core/frame/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.
 
 """Blink frame presubmit script
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 56 matching lines @@
     source_path = ''
     for f in input_api.AffectedFiles():
         if f.LocalPath().endswith('UseCounter.h'):
             source_path = f.LocalPath()
             break
     else:
         return []
 
     START_MARKER = '^enum Feature : uint32_t {'
     END_MARKER = '^NumberOfFeatures'
-    if update_histogram_enum.HistogramNeedsUpdate(
-            histogram_enum_name='FeatureObserver',
-            source_enum_path=source_path,
-            start_marker=START_MARKER,
-            end_marker=END_MARKER):
+    should_update_histogram, duplicated_values = update_histogram_enum.HistogramNeedsUpdate(

[Ilya Sherman, 2017/04/13 01:12:49]

Should this wrap to 80-col?

+        histogram_enum_name='FeatureObserver',
+        source_enum_path=source_path,
+        start_marker=START_MARKER,
+        end_marker=END_MARKER)
+    if duplicated_values:
+        return [output_api.PresubmitPromptWarning(
+            'UseCounter::Feature has been updated and there exists duplicated '
+            'values between (%s) and (%s)' % duplicated_values,
+            items=[source_path])]
+    if should_update_histogram:
         return [output_api.PresubmitPromptWarning(
             'UseCounter::Feature has been updated and the UMA mapping needs to '
             'be regenerated. Please run update_use_counter_feature_enum.py in '
             'src/tools/metrics/histograms/ to update the mapping.',
             items=[source_path])]
 
     return []
 
 
 def CheckChangeOnUpload(input_api, output_api):
     results = []
     results.extend(_RunUseCounterChecks(input_api, output_api))
     results.extend(_RunUmaHistogramChecks(input_api, output_api))
     return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
     results = []
     results.extend(_RunUseCounterChecks(input_api, output_api))
     results.extend(_RunUmaHistogramChecks(input_api, output_api))
     return results