Remove kDistroDict from Preferences.

chrome/installer/util/master_preferences.h

Index: chrome/installer/util/master_preferences.h
diff --git a/chrome/installer/util/master_preferences.h b/chrome/installer/util/master_preferences.h
index 4c5704869d04f9b7339d2a4818bfacea1cb27fea..9807d9f73fca996e35ad95796083c2c06c84f60f 100644
--- a/chrome/installer/util/master_preferences.h
+++ b/chrome/installer/util/master_preferences.h
@@ -43,7 +43,6 @@ const char kDefaultMasterPrefs[] = "master_preferences";
 //      "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,