Address some TODO(GYP_GONE)s

ui/vector_icons/aggregate_vector_icons.py

 # Copyright 2015 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.
 
 import fileinput
 import glob
 import optparse
 import os
 import shlex
 import sys
 import textwrap
 
 def AggregateVectorIconsLegacy(working_directory, file_list, output_cc,
                                output_h):
   icon_list = []
-  if file_list is None:
-    # TODO(GYP_GONE): |file_list| is only None for GYP builds (where response
-    # files are not supported), in which case we process all .icon files
-    # contained within |working_directory| and all of its descendant
-    # directories. This logic can be removed when GN is used everywhere.
-    # See crbug.com/535386.
-    for dirpath, dirnames, filenames in os.walk(working_directory):
-      icon_list.extend(glob.glob(os.path.join(dirpath, "*.icon")))
-  else:
-    with open(file_list, 'r') as f:
-      file_list_contents = f.read()
-    icon_list = shlex.split(file_list_contents)
+  assert file_list is not None
+  with open(file_list, 'r') as f:
+    file_list_contents = f.read()
+  icon_list = shlex.split(file_list_contents)
 
   input_header_template = open(os.path.join(working_directory,
                                             "vector_icons.h.template"))
   header_template_contents = input_header_template.readlines()
   input_header_template.close()
   output_header = open(output_h, "w")
   for line in header_template_contents:
     if not "TEMPLATE_PLACEHOLDER" in line:
       output_header.write(line)
       continue
@@ skipping 189 matching lines @@
 
   AggregateVectorIcons(options.working_directory,
                        options.file_list,
                        options.output_cc,
                        options.output_h,
                        options.use_legacy_template)
 
 
 if __name__ == "__main__":
   main()