Remove kDistroDict from Preferences.

chrome/installer/util/master_preferences.h

 // 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.
 //
 // This file contains functions processing master preference file used by
 // setup and first run.
 
 #ifndef CHROME_INSTALLER_UTIL_MASTER_PREFERENCES_H_
 #define CHROME_INSTALLER_UTIL_MASTER_PREFERENCES_H_
 
@@ skipping 25 matching lines @@
 // A prototypical 'master_preferences' file looks like this:
 //
 // {
 //   "distribution": {
 //      "create_all_shortcuts": true,
 //      "import_bookmarks": false,
 //      "import_bookmarks_from_file": "c:\\path",
 //      "import_history": false,
 //      "import_home_page": false,
 //      "import_search_engine": true,
-//      "ping_delay": 40,

[grt (UTC plus 2), 2017/02/24 07:42:21]

isn't this still the proper way to set the ping_delay?

[Roger Tawa OOO till Jul 10th, 2017/02/24 16:02:18]

Agreed.  Until the docs are changed, everyone will continue to use this method. 
So we need to make sure it still works all the time.

[gab, 2017/02/28 19:54:45]

Good point (and I'm not signing up to update any docs -- just wanted to
straighten the master pref versus runtime Preferences story, I'm fine keeping
this first run mapping virtually forever).

 //      "show_welcome_page": true,
 //      "skip_first_run_ui": true,
 //      "do_not_launch_chrome": false,
 //      "make_chrome_default": false,
 //      "make_chrome_default_for_user": true,
 //      "require_eula": true,
 //      "system_level": false,
 //      "verbose_logging": true,
 //      "welcome_page_on_os_upgrade_enabled": false
 //   },
@@ skipping 145 matching lines @@
   base::DictionaryValue* distribution_ = nullptr;
   bool preferences_read_from_file_ = false;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MasterPreferences);
 };
 
 }  // namespace installer
 
 #endif  // CHROME_INSTALLER_UTIL_MASTER_PREFERENCES_H_