Clean up histograms.xml formatting

tools/metrics/histograms/extract_histograms.py

 # Copyright 2013 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.
 
 """Extract histogram names from the description XML file.
 
 For more information on the format of the XML file, which is self-documenting,
 see histograms.xml; however, here is a simple example to get you started. The
 XML below will generate the following five histograms:
 
@@ skipping 21 matching lines @@
 <enums>
 
 <enum name="MyEnumType">
   <summary>This is an example enum type, where the values mean little.</summary>
   <int value="1" label="FIRST_VALUE">This is the first value.</int>
   <int value="2" label="SECOND_VALUE">This is the second value.</int>
 </enum>
 
 </enums>
 
-<histogram_suffixes_list>
+<histogram-suffixes-list>
 
-<histogram_suffixes name="BrowserType">
+<histogram-suffixes name="BrowserType">
   <suffix name="Chrome"/>
   <suffix name="IE"/>
   <suffix name="Firefox"/>
   <affected-histogram name="HistogramEnum"/>
-</histogram_suffixes>
+</histogram-suffixes>
 
-</histogram_suffixes_list>
+</histogram-suffixes-list>
 
 </histogram-configuration>
 
 """
 
 import bisect
 import copy
 import logging
 import xml.dom.minidom
 
@@ skipping 115 matching lines @@
 
 
 def _ExtractEnumsFromXmlTree(tree):
   """Extract all <enum> nodes in the tree into a dictionary."""
 
   enums = {}
   have_errors = False
 
   last_name = None
   for enum in tree.getElementsByTagName('enum'):
-    if enum.getAttribute('type') != 'int':
-      logging.error('Unknown enum type %s', enum.getAttribute('type'))
-      have_errors = True
-      continue
-
     name = enum.getAttribute('name')
     if last_name is not None and name.lower() < last_name.lower():
       logging.error('Enums %s and %s are not in alphabetical order',
                     last_name, name)
       have_errors = True
     last_name = name
 
     if name in enums:
       logging.error('Duplicate enum %s', name)
       have_errors = True
@@ skipping 322 matching lines @@
     tree = xml.dom.minidom.parse(f)
     histograms, had_errors = ExtractHistogramsFromDom(tree)
     if had_errors:
       logging.error('Error parsing %s', filename)
       raise Error()
     return histograms
 
 
 def ExtractNames(histograms):
   return sorted(histograms.keys())