Make histogram_suffixes separators and enum labels required.

tools/metrics/histograms/print_style.py

Index: tools/metrics/histograms/print_style.py
diff --git a/tools/metrics/histograms/print_style.py b/tools/metrics/histograms/print_style.py
index 6b7064990c6141bb812ef69f4b3361a0c8ac26ca..4e5efa1ffc8d61514dacb49e69b6b3e9f0557c49 100644
--- a/tools/metrics/histograms/print_style.py
+++ b/tools/metrics/histograms/print_style.py
@@ -32,6 +32,15 @@ ATTRIBUTE_ORDER = {
     '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',
@@ -72,6 +81,7 @@ TAGS_ALPHABETIZATION_RULES = {
 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,