Introduce a new framework for back-and-forth tracked/protected preferences migration.

chrome/chrome_browser.gypi

 # Copyright 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 1590 matching lines @@
         'browser/prefs/tracked/pref_hash_calculator_helper_win.cc',
         'browser/prefs/tracked/pref_service_hash_store_contents.cc',
         'browser/prefs/tracked/pref_service_hash_store_contents.h',
         'browser/prefs/tracked/segregated_pref_store.cc',
         'browser/prefs/tracked/segregated_pref_store.h',
         'browser/prefs/tracked/tracked_atomic_preference.cc',
         'browser/prefs/tracked/tracked_atomic_preference.h',
         'browser/prefs/tracked/tracked_preference.h',
         'browser/prefs/tracked/tracked_preference_helper.cc',
         'browser/prefs/tracked/tracked_preference_helper.h',
+        'browser/prefs/tracked/tracked_preferences_migration.cc',
+        'browser/prefs/tracked/tracked_preferences_migration.h',
         'browser/prefs/tracked/tracked_split_preference.cc',
         'browser/prefs/tracked/tracked_split_preference.h',
         'browser/prerender/external_prerender_handler_android.cc',
         'browser/prerender/external_prerender_handler_android.h',
         'browser/prerender/prerender_condition.h',
         'browser/prerender/prerender_config.cc',
         'browser/prerender/prerender_config.h',
         'browser/prerender/prerender_contents.cc',
         'browser/prerender/prerender_contents.h',
         'browser/prerender/prerender_events.cc',
@@ skipping 2096 matching lines @@
             'package_name': 'org/chromium/chrome/browser',
             'template_deps': ['browser/android/tab_load_status.h'],
           },
           'includes': [ '../build/android/java_cpp_template.gypi' ],
         },
       ],
      },
     ],
   ],
 }