Add more components to the GN build.

components/network_time.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/network_time
       'target_name': 'network_time',
       'type': 'static_library',
       'dependencies': [
         '../base/base.gyp:base',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'network_time/network_time_tracker.cc',
         'network_time/network_time_tracker.h',
         'network_time/network_time_pref_names.cc',
         'network_time/network_time_pref_names.h',
       ],
     },
   ],
 }