Remove old default search preferences.

components/user_prefs/tracked/pref_hash_filter.cc

Index: components/user_prefs/tracked/pref_hash_filter.cc
diff --git a/components/user_prefs/tracked/pref_hash_filter.cc b/components/user_prefs/tracked/pref_hash_filter.cc
index 1101080cd76db95717be6db8ce0a73c33afe465e..b42e9f3799a1ba41b7ae429f49b5bbd42c27bf91 100644
--- a/components/user_prefs/tracked/pref_hash_filter.cc
+++ b/components/user_prefs/tracked/pref_hash_filter.cc
@@ -39,7 +39,11 @@ void CleanupDeprecatedTrackedPreferences(
       // TODO(mad): Remove in M48+.
       "software_reporter.prompt_reason",
       // TODO(zea): Remove in M52+,
-      "sync.remaining_rollback_tries"
+      "sync.remaining_rollback_tries",

[gab, 2016/12/23 17:26:26]

Remove the above entries (since people tend to forget we do a rolling cleanup
where the next person cleans the previous person's entries :)).

[Alexander Yashkin, 2016/12/23 20:28:13]

Done

+      // TODO(a-v-y): Remove after M59.

[gab, 2016/12/23 17:26:26]

"Remove in M60+." (i.e. we like to leave the cleanup for a good 3+ milestones)

[Alexander Yashkin, 2016/12/23 20:28:13]

Done

+      "default_search_provider.search_url",

[Alexander Yashkin, 2016/12/23 12:03:23]

@gab
I have added deprecated tracked prefs here to cleanup, yet I am not sure if its
needed.
This function removes deprecated prefs by calling:

 pref_store_contents->Remove(key, NULL);
 hash_store_transaction->ClearHash(key);

In migration logic old preferences were always cleared from prefs after
migrating to new set.
Can I simply remove them without cleanup?

[gab, 2016/12/23 17:26:26]

You can remove the prefs' constants themselves (and their entry in
kTrackedPrefs). But you will still need this to cleanup up the MAC associated
with an (hopefully by now) null pref.

[Alexander Yashkin, 2016/12/23 20:28:13]

Done

+      "default_search_provider.name",
+      "default_search_provider.keyword"
   };
 
   for (size_t i = 0; i < arraysize(kDeprecatedTrackedPreferences); ++i) {