Readdress use_counter_feature_enum issue

tools/metrics/histograms/update_histogram_enum.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.
 
 """Updates enums in histograms.xml file with values read from provided C++ enum.
 
 If the file was pretty-printed, the updated version is pretty-printed too.
 """
 
 import logging
@@ skipping 15 matching lines @@
 
 class UserError(Exception):
   def __init__(self, message):
     Exception.__init__(self, message)
 
   @property
   def message(self):
     return self.args[0]
 
 
+class DuplicatedValue(Exception):
+  """Exception raised for duplicated enum values.
+
+  Attributes:
+      first_label: First enum label that shares the duplicated enum value.
+      second_label: Second enum label that shares the duplicated enum value.
+  """
+  def __init__(self, first_label, second_label):
+    self.first_label = first_label
+    self.second_label = second_label
+
+
 def Log(message):
   logging.info(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.
+  """Creates a dictionary of enum values, read from a C++ file.
 
   Args:
       filename: The unix-style path (relative to src/) of the file to open.
       start_marker: A regex that signifies the start of the enum values.
       end_marker: A regex that signifies the end of the enum values.
       strip_k_prefix: Set to True if enum values are declared as kFoo and the
           'k' should be stripped.
+
+  Returns:
+      A boolean indicating wheather the histograms.xml file would be changed.
+
+  Raises:
+      DuplicatedValue: An error when two enum labels share the same value.
   """
   # Read the file as a list of lines
   with open(path_util.GetInputFile(filename)) as f:
     content = f.readlines()
 
   START_REGEX = re.compile(start_marker)
   ITEM_REGEX = re.compile(r'^(\w+)')
   ITEM_REGEX_WITH_INIT = re.compile(r'(\w+)\s*=\s*(\d*)')
   WRAPPED_INIT = re.compile(r'(\d+)')
   END_REGEX = re.compile(end_marker)
@@ skipping 25 matching lines @@
       m = ITEM_REGEX.match(line)
       if m:
         label = m.group(1)
       else:
         continue
     if strip_k_prefix:
       assert label.startswith('k'), "Enum " + label + " should start with 'k'."
       label = label[1:]
     # If two enum labels have the same value
     if enum_value in result:
-      return result, (result[enum_value], label)
+      raise DuplicatedValue(result[enum_value], label)
     result[enum_value] = label
     enum_value += 1
-  return result, None
+  return result
 
 
 def CreateEnumItemNode(document, value, label):
   """Creates an int element to append to an enum."""
   item_node = document.createElement('int')
   item_node.attributes['value'] = str(value)
   item_node.attributes['label'] = label
   return item_node
 
 
@@ skipping 86 matching lines @@
           the C++ header file from which to read the enum.
       start_marker: A regular expression that matches the start of the C++ enum.
       end_marker: A regular expression that matches the end of the C++ enum.
       strip_k_prefix: Set to True if enum values are declared as kFoo and the
           'k' should be stripped.
 
   Returns:
       A string with presubmit failure description, or None (if no failures).
   """
   Log('Reading histogram enum definition from "{0}".'.format(source_enum_path))
-  source_enum_values, duplicated_values = ReadHistogramValues(
-      source_enum_path, start_marker, end_marker, strip_k_prefix)
-
-  if duplicated_values:
+  try:
+    source_enum_values = ReadHistogramValues(
+        source_enum_path, start_marker, end_marker, strip_k_prefix)
+  except DuplicatedValue as duplicated_values:
     return ('%s enum has been updated and there exist '
-            'duplicated values between (%s) and (%s)' % (histogram_enum_name,
-                                                         duplicated_values[0],
-                                                         duplicated_values[1]))
+            'duplicated values between (%s) and (%s)' %
+            (histogram_enum_name, duplicated_values.first_label,
+             duplicated_values.second_label))
 
   (xml, new_xml) = _GetOldAndUpdatedXml(histogram_enum_name, source_enum_values,
                                         source_enum_path)
   if xml != new_xml:
     return ('%s enum has been updated and the UMA mapping needs to be '
             'regenerated. Please run %s in src/tools/metrics/histograms/ to '
             'update the mapping.' % (histogram_enum_name, update_script_name))
 
   return None
 
@@ skipping 31 matching lines @@
       strip_k_prefix: Set to True if enum values are declared as kFoo and the
           'k' should be stripped.
   """
 
   Log('Reading histogram enum definition from "{0}".'.format(source_enum_path))
   source_enum_values, ignored = ReadHistogramValues(source_enum_path,
       start_marker, end_marker, strip_k_prefix)
 
   UpdateHistogramFromDict(histogram_enum_name, source_enum_values,
       source_enum_path)