Remove obsolete fieldtrial related code.

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 24 matching lines @@
   <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 name="BrowserType">
-  <group name="Chrome"/>
-  <group name="IE"/>
-  <group name="Firefox"/>
+  <suffix name="Chrome"/>
+  <suffix name="IE"/>
+  <suffix name="Firefox"/>
   <affected-histogram name="HistogramEnum"/>
 </histogram_suffixes>
 
 </histogram_suffixes_list>
 
 </histogram-configuration>
 
 """
 
 import copy
@@ skipping 242 matching lines @@
 
   Args:
     tree: XML dom tree.
     histograms: a dictionary of histograms previously extracted from the tree;
 
   Returns:
     True if any errors were found.
   """
   have_errors = False
 
-  # TODO(yiyaoliu): Remove this part after fieldtrial is not used any more.
-  if tree.getElementsByTagName('histogram_suffixes'):
-    histogram_suffix_tag = 'histogram_suffixes'
-    suffix_tag = 'suffix'
-    with_tag = 'with-suffix'
-  else:
-    histogram_suffix_tag = 'fieldtrial'
-    suffix_tag = 'group'
-    with_tag = 'with-group'
+  histogram_suffix_tag = 'histogram_suffixes'
+  suffix_tag = 'suffix'
+  with_tag = 'with-suffix'
 
   # Verify order of histogram_suffixes fields first.
   last_name = None
   for histogram_suffixes in tree.getElementsByTagName(histogram_suffix_tag):
     name = histogram_suffixes.getAttribute('name')
     if last_name is not None and name.lower() < last_name.lower():
       logging.error('histogram_suffixes %s and %s are not in alphabetical '
                     'order', last_name, name)
       have_errors = True
     last_name = name
@@ skipping 129 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())