Readdress use_counter_feature_enum issue

tools/metrics/histograms/update_histogram_enum.py

Index: tools/metrics/histograms/update_histogram_enum.py
diff --git a/tools/metrics/histograms/update_histogram_enum.py b/tools/metrics/histograms/update_histogram_enum.py
index f0a29e0fe91c7aaf1c0500e82c572c0d836c4059..9cd55ff997280dcd59045b38aa5f26b0f92cdf78 100644
--- a/tools/metrics/histograms/update_histogram_enum.py
+++ b/tools/metrics/histograms/update_histogram_enum.py
@@ -38,8 +38,8 @@ def Log(message):
 
 
 def ReadHistogramValues(filename, start_marker, end_marker, strip_k_prefix):
-  """Returns a dictionary of enum values and a pair of labels that have the same
-     enum values, read from a C++ file.
+  """Returns a dictionary of enum values, read from a C++ file; or raises an
+     exception if a pair of labels have the same enum values.
 
   Args:
       filename: The unix-style path (relative to src/) of the file to open.
@@ -89,13 +89,13 @@ def ReadHistogramValues(filename, start_marker, end_marker, strip_k_prefix):
         continue
     # If two enum labels have the same value
     if enum_value in result:
-      return result, (result[enum_value], label)
+      raise Exception(result[enum_value], label)
     if strip_k_prefix:
       assert label.startswith('k'), "Enum " + label + " should start with 'k'."
       label = label[1:]
     result[enum_value] = label
     enum_value += 1
-  return result, None
+  return result
 
 
 def CreateEnumItemNode(document, value, label):