Create 'errors' histogram for failures.

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 124 matching lines @@
   """
   if histogram_suffixes_node.hasAttribute('separator'):
     separator = histogram_suffixes_node.getAttribute('separator')
   else:
     separator = '_'
 
   if histogram_suffixes_node.hasAttribute('ordering'):
     ordering = histogram_suffixes_node.getAttribute('ordering')
   else:
     ordering = 'suffix'
+  parts = ordering.split(',')

[Alexei Svitkine (slow), 2017/01/18 18:46:59]

Note: Please also make the same change in the internal copy of this code. Will
send you a link separately.

[bcwhite, 2017/01/18 19:06:59]

Acknowledged.

+  ordering = parts[0]
+  if len(parts) > 1:
+    placement = int(parts[1])
+  else:
+    placement = 1
   if ordering not in ['prefix', 'suffix']:
     logging.error('ordering needs to be prefix or suffix, value is %s',
                   ordering)
     raise Error()
 
   if not suffix_name:
     return histogram_name
 
   if ordering == 'suffix':
     return histogram_name + separator + suffix_name
 
   # For prefixes, the suffix_name is inserted between the "cluster" and the
   # "remainder", e.g. Foo.BarHist expanded with gamma becomes Foo.gamma_BarHist.
   sections = histogram_name.split('.')
-  if len(sections) <= 1:
+  if len(sections) <= placement:
     logging.error(
         'Prefix Field Trial expansions require histogram names which include a '

[Alexei Svitkine (slow), 2017/01/18 18:46:59]

Nit: Rename this message to not say "Field Trial".

i.e. "Prefix histogram_suffixes expansions..."

also the second place on line 168.

[bcwhite, 2017/01/18 19:06:59]

Done.

-        'dot separator. Histogram name is %s, and Field Trial is %s',
-        histogram_name, histogram_suffixes_node.getAttribute('name'))
+        'dot separator. Histogram name is %s, Field Trial is %s, and placment '
+        'is %d', histogram_name, histogram_suffixes_node.getAttribute('name'),
+        placement)
     raise Error()
 
-  cluster = sections[0] + '.'
-  remainder = '.'.join(sections[1:])
+  cluster = '.'.join(sections[0:placement]) + '.'
+  remainder = '.'.join(sections[placement:])
   return cluster + suffix_name + separator + remainder
 
 
 def _ExtractEnumsFromXmlTree(tree):
   """Extract all <enum> nodes in the tree into a dictionary."""
 
   enums = {}
   have_errors = False
 
   last_name = None
@@ skipping 324 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())