Make histogram_suffixes separators and enum labels required.

tools/metrics/histograms/print_style.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.
 
 """Holds the constants for pretty printing histograms.xml."""
 
 import os
 import sys
 
 # Import the metrics/common module for pretty print xml.
@@ skipping 14 matching lines @@
     'histogram_suffixes_list': [],
     'histograms': [],
     'int': ['value', 'label'],
     'obsolete': [],
     'owner': [],
     'suffix': ['base', 'name', 'label'],
     'summary': [],
     'with-suffix': ['name'],
 }
 
+# Attribute names that must be explicitly specified on nodes that support them.
+REQUIRED_ATTRIBUTES = [
+    # TODO(isherman): Make the 'label' attribute required as well. This requires
+    # fixing up existing suffixes that omit a label.
+    'name',
+    'separator',
+    'value',
+]
+
 # Tag names for top-level nodes whose children we don't want to indent.
 TAGS_THAT_DONT_INDENT = [
     'histogram-configuration',
     'histograms',
     'histogram_suffixes_list',
     'enums',
 ]
 
 # Extra vertical spacing rules for special tag names.
 # {tag_name: (newlines_after_open, newlines_before_close, newlines_after_close)}
@@ skipping 20 matching lines @@
     'enums': ('enum', LOWERCASE_NAME_FN),
     'enum': ('int', lambda n: int(n.attributes['value'].value)),
     'histogram_suffixes_list': ('histogram_suffixes', LOWERCASE_NAME_FN),
     'histogram_suffixes': ('affected-histogram', LOWERCASE_NAME_FN),
 }
 
 
 def GetPrintStyle():
   """Returns an XmlStyle object for pretty printing histograms."""
   return pretty_print_xml.XmlStyle(ATTRIBUTE_ORDER,
+                                   REQUIRED_ATTRIBUTES,
                                    TAGS_THAT_HAVE_EXTRA_NEWLINE,
                                    TAGS_THAT_DONT_INDENT,
                                    TAGS_THAT_ALLOW_SINGLE_LINE,
                                    TAGS_ALPHABETIZATION_RULES)