Add support for base histograms in histograms.xml.

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 45 matching lines @@
 
 import copy
 import logging
 import xml.dom.minidom
 
 OWNER_FIELD_PLACEHOLDER = (
     'Please list the metric\'s owners. Add more owner tags as needed.')
 
 MAX_HISTOGRAM_SUFFIX_DEPENDENCY_DEPTH = 5
 
+DEFAULT_BASE_HISTOGRAM_OBSOLETE_REASON = (
+    'Base histogram. Use suffixes of this histogram instead.')
+
 
 class Error(Exception):
   pass
 
 
 def _JoinChildNodes(tag):
   """Join child nodes into a single text.
 
   Applicable to leafs like 'summary' and 'detail'.
 
@@ skipping 147 matching lines @@
 def _ExtractOwners(xml_node):
   """Extract all owners into a list from owner tag under |xml_node|."""
   owners = []
   for owner_node in xml_node.getElementsByTagName('owner'):
     owner_entry = _NormalizeString(_JoinChildNodes(owner_node))
     if OWNER_FIELD_PLACEHOLDER not in owner_entry:
       owners.append(owner_entry)
   return owners
 
 
+def _ProcessBaseHistogramAttribute(node, histogram_entry):
+  if node.hasAttribute('base'):
+    is_base = node.getAttribute('base').lower() == 'true'
+    histogram_entry['base'] = is_base
+    if is_base and 'obsolete' not in histogram_entry:
+      histogram_entry['obsolete'] = DEFAULT_BASE_HISTOGRAM_OBSOLETE_REASON
+
+
 def _ExtractHistogramsFromXmlTree(tree, enums):
   """Extract all <histogram> nodes in the tree into a dictionary."""
 
   # Process the histograms. The descriptions can include HTML tags.
   histograms = {}
   have_errors = False
   last_name = None
   for histogram in tree.getElementsByTagName('histogram'):
     name = histogram.getAttribute('name')
     if last_name is not None and name.lower() < last_name.lower():
@@ skipping 38 matching lines @@
 
     # Handle enum types.
     if histogram.hasAttribute('enum'):
       enum_name = histogram.getAttribute('enum')
       if enum_name not in enums:
         logging.error('Unknown enum %s in histogram %s', enum_name, name)
         have_errors = True
       else:
         histogram_entry['enum'] = enums[enum_name]
 
+    _ProcessBaseHistogramAttribute(histogram, histogram_entry)
+
   return histograms, have_errors
 
 
 # Finds an <obsolete> node amongst |node|'s immediate children and returns its
 # content as a string. Returns None if no such node exists.
 def _GetObsoleteReason(node):
   for child in node.childNodes:
     if child.localName == 'obsolete':
       # There can be at most 1 obsolete element per node.
       return _JoinChildNodes(child)
@@ skipping 90 matching lines @@
       if with_suffixes:
         suffixes_to_add = with_suffixes
       else:
         suffixes_to_add = suffix_nodes
       for suffix in suffixes_to_add:
         suffix_name = suffix.getAttribute('name')
         try:
           new_histogram_name = _ExpandHistogramNameWithSuffixes(
               suffix_name, histogram_name, histogram_suffixes)
           if new_histogram_name != histogram_name:
-            histograms[new_histogram_name] = copy.deepcopy(
-                histograms[histogram_name])
+            new_histogram = copy.deepcopy(histograms[histogram_name])
+            # Do not copy forward base histogram state to suffixed
+            # histograms. Any suffixed histograms that wish to remain base
+            # histograms must explicitly re-declare themselves as base
+            # histograms.
+            if new_histogram.get('base', False):
+              del new_histogram['base']
+              if (new_histogram.get('obsolete', '') ==
+                  DEFAULT_BASE_HISTOGRAM_OBSOLETE_REASON):
+                del new_histogram['obsolete']
+            histograms[new_histogram_name] = new_histogram
 
           suffix_label = suffix_labels.get(suffix_name, '')
 
           # TODO(yiyaoliu): Rename these to be consistent with the new naming.
           # It is kept unchanged for now to be it's used by dashboards.
           if 'fieldtrial_groups' not in histograms[new_histogram_name]:
             histograms[new_histogram_name]['fieldtrial_groups'] = []
           histograms[new_histogram_name]['fieldtrial_groups'].append(
               suffix_name)
 
@@ skipping 16 matching lines @@
           # group itself was obsolete as well.
           obsolete_reason = _GetObsoleteReason(suffix)
           if not obsolete_reason:
             obsolete_reason = group_obsolete_reason
 
           # If the suffix has an obsolete tag, all histograms it generates
           # inherit it.
           if obsolete_reason:
             histograms[new_histogram_name]['obsolete'] = obsolete_reason
 
+          _ProcessBaseHistogramAttribute(suffix, histograms[new_histogram_name])
+
         except Error:
           have_errors = True
 
   return have_errors
 
 
 def ExtractHistogramsFromFile(file_handle):
   """Compute the histogram names and descriptions from the XML representation.
 
   Args:
@@ skipping 29 matching lines @@
   with open(filename, 'r') as f:
     histograms, had_errors = ExtractHistogramsFromFile(f)
     if had_errors:
       logging.error('Error parsing %s', filename)
       raise Error()
     return histograms
 
 
 def ExtractNames(histograms):
   return sorted(histograms.keys())