Correct ChildAccountService child flag retrieval

This CL fixes two bugs in ChildAccountService's child flag retrieval:
* When flag fetching is disabled by command-line flag, causing all
  accounts to be marked as non-child, the flag status should be set
  to "known," not "unknown."
* When the flag is retrieved from the cloud, it should be stored
  before notifying callbacks waiting for the retrieval to finish.

This CL is a prerequisite for the test in crbug.com/477145.

BUG=477145
TEST=Tested as part of the new browser test in follow-up CL

Review URL: https://codereview.chromium.org/1051273009

Cr-Commit-Position: refs/heads/master@{#326058}

chrome/browser/supervised_user/child_accounts/child_account_service.cc

@@ -103,15 +103,19 @@ void ChildAccountService::RegisterProfilePrefs(
 
 void ChildAccountService::SetIsChildAccount(bool is_child_account) {
   PropagateChildStatusToUser(is_child_account);
-  if (profile_->IsChild() == is_child_account)
-    return;
-
-  if (is_child_account) {
-    profile_->GetPrefs()->SetString(prefs::kSupervisedUserId,
-                                    supervised_users::kChildAccountSUID);
-  } else {
-    profile_->GetPrefs()->ClearPref(prefs::kSupervisedUserId);
+  if (profile_->IsChild() != is_child_account) {
+    if (is_child_account) {
+      profile_->GetPrefs()->SetString(prefs::kSupervisedUserId,
+                                      supervised_users::kChildAccountSUID);
+    } else {
+      profile_->GetPrefs()->ClearPref(prefs::kSupervisedUserId);
+    }
   }
+  profile_->GetPrefs()->SetBoolean(prefs::kChildAccountStatusKnown, true);
+
+  for (const auto& callback : status_received_callback_list_)
+    callback.Run();
+  status_received_callback_list_.clear();
 }
 
 void ChildAccountService::Init() {
@@ -321,16 +325,6 @@ void ChildAccountService::OnFlagsFetched(
       std::find(flags.begin(), flags.end(),
                 kIsChildAccountServiceFlagName) != flags.end();
 
-  bool status_was_known = profile_->GetPrefs()->GetBoolean(
-      prefs::kChildAccountStatusKnown);
-  profile_->GetPrefs()->SetBoolean(prefs::kChildAccountStatusKnown, true);
-
-  if (!status_was_known) {
-    for (auto& callback : status_received_callback_list_)
-      callback.Run();
-    status_received_callback_list_.clear();
-  }
-
   SetIsChildAccount(is_child_account);
 
   ScheduleNextStatusFlagUpdate(