Revamp the MigrateBrowserPrefs and MigrateUserPrefs code.

chrome/chrome_browser_chromeos.gypi

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     # These files lists are shared with the GN build.
     'browser_chromeos_sources': [
         # All .cc, .h, .m, and .mm files under browser/chromeos, except for tests
@@ skipping 401 matching lines @@
         'browser/chromeos/login/app_launch_signin_screen.cc',
         'browser/chromeos/login/app_launch_signin_screen.h',
         'browser/chromeos/login/auth/auth_prewarmer.cc',
         'browser/chromeos/login/auth/auth_prewarmer.h',
         'browser/chromeos/login/auth/chrome_cryptohome_authenticator.cc',
         'browser/chromeos/login/auth/chrome_cryptohome_authenticator.h',
         'browser/chromeos/login/auth/chrome_login_performer.cc',
         'browser/chromeos/login/auth/chrome_login_performer.h',
         'browser/chromeos/login/chrome_restart_request.cc',
         'browser/chromeos/login/chrome_restart_request.h',
-        'browser/chromeos/login/default_pinned_apps_field_trial.cc',
-        'browser/chromeos/login/default_pinned_apps_field_trial.h',
         'browser/chromeos/login/demo_mode/demo_app_launcher.cc',
         'browser/chromeos/login/demo_mode/demo_app_launcher.h',
         'browser/chromeos/login/easy_unlock/easy_unlock_create_keys_operation.cc',
         'browser/chromeos/login/easy_unlock/easy_unlock_create_keys_operation.h',
         'browser/chromeos/login/easy_unlock/easy_unlock_get_keys_operation.cc',
         'browser/chromeos/login/easy_unlock/easy_unlock_get_keys_operation.h',
         'browser/chromeos/login/easy_unlock/easy_unlock_key_manager.cc',
         'browser/chromeos/login/easy_unlock/easy_unlock_key_manager.h',
         'browser/chromeos/login/easy_unlock/easy_unlock_reauth.cc',
         'browser/chromeos/login/easy_unlock/easy_unlock_reauth.h',
@@ skipping 860 matching lines @@
         'browser/chromeos/attestation/attestation_signed_data.proto',
       ],
       'variables': {
         'proto_in_dir': 'browser/chromeos/attestation',
         'proto_out_dir': 'chrome/browser/chromeos/attestation',
       },
       'includes': [ '../build/protoc.gypi' ]
     },
   ],
 }