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

third_party/WebKit/Source/core/frame/PRESUBMIT.py

Index: third_party/WebKit/Source/core/frame/PRESUBMIT.py
diff --git a/third_party/WebKit/Source/core/frame/PRESUBMIT.py b/third_party/WebKit/Source/core/frame/PRESUBMIT.py
index ec96ed48c28a962f47e9236a9d20c60028f324c5..bf99bac13f2cd232d9b9a3c7cd827252048d0b4a 100644
--- a/third_party/WebKit/Source/core/frame/PRESUBMIT.py
+++ b/third_party/WebKit/Source/core/frame/PRESUBMIT.py
@@ -74,22 +74,23 @@ def _RunUmaHistogramChecks(input_api, output_api):
 
     start_marker = '^enum Feature : uint32_t {'
     end_marker = '^kNumberOfFeatures'
-    should_update_histogram, duplicated_values = update_histogram_enum.HistogramNeedsUpdate(
-        histogram_enum_name='FeatureObserver',
-        source_enum_path=source_path,
-        start_marker=start_marker,
-        end_marker=end_marker,
-        strip_k_prefix=True)
-    if duplicated_values:
+    try:
+        if update_histogram_enum.HistogramNeedsUpdate(
+                histogram_enum_name='FeatureObserver',
+                source_enum_path=source_path,
+                start_marker=start_marker,
+                end_marker=end_marker,
+                strip_k_prefix=True):
+            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])]
+    except Exception as duplicated_value:   # pylint: disable=W0703
         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.',
+            'values between (%s) and (%s)' % duplicated_value.args,
             items=[source_path])]
 
     return []