Remove uses of deprecated RegisterDictionaryPref

The override of RegisterDictionaryPref taking a std::unique_ptr<base::Value>
is deprecated in favor of the method taking the base::Value by value.

Convert client code to either not pass default value if the value is just
an empty dictionary (as there is an override doing this). If the dictionary
is not empty, convert the code to create and pass it by value.

This CL was uploaded by git cl split.

Bug: 646113
Change-Id: I619acaf4e1edf4741ad5d696fc9945659baecdcf
Reviewed-on: https://chromium-review.googlesource.com/c/1454526
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629192}

chrome/browser/chromeos/login/easy_unlock/easy_unlock_service.cc

@@ -213,9 +213,7 @@ EasyUnlockService::~EasyUnlockService() {}
 // static
 void EasyUnlockService::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
-  registry->RegisterDictionaryPref(prefs::kEasyUnlockPairing,
-                                   std::make_unique<base::DictionaryValue>());
-
+  registry->RegisterDictionaryPref(prefs::kEasyUnlockPairing);
   proximity_auth::ProximityAuthProfilePrefManager::RegisterPrefs(registry);
 }