Add more components to GN build.

components/url_fixer.gypi

 # Copyright 2014 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.
 
 {
   'targets': [
     {
+      # GN version: //components/url_fixer
       'target_name': 'url_fixer',
       'type': 'static_library',
       'include_dirs': [
         '..',
       ],
       'dependencies': [
         '../base/base.gyp:base',
         '../net/net.gyp:net',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'url_fixer/url_fixer.cc',
         'url_fixer/url_fixer.h',
       ],
       # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
       'msvs_disabled_warnings': [4267, ],
     },
   ],
 }