Enforce ARC_PACKAGE datatype for supervised users

GetForcedDataTypes() for supervised users used to return all datatypes
controlled by APPS user settings except ARC_PACKAGE. We are going to
introduce new enum for UserSelectableTypes() and this function should
return this enum after refactoring. It means, that after refactoring
ARC_PACKAGE will be enforced by putting APPS in the result.

Absence of ARC_PACKAGE in old result of GetForcedDataTypes() should
be a bug.

Bug: 906611
Change-Id: I8a5ef8cca7ac442529723b8e445924b9b22cef4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1564110Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Maksim Moskvitin <mmoskvitin@google.com>
Cr-Commit-Position: refs/heads/master@{#649835}

chrome/browser/supervised_user/supervised_user_service.cc

@@ -979,6 +979,7 @@ syncer::ModelTypeSet SupervisedUserService::GetForcedDataTypes() const {
   result.Put(syncer::APPS);
   result.Put(syncer::APP_SETTINGS);
   result.Put(syncer::APP_LIST);
+  result.Put(syncer::ARC_PACKAGE);
   return result;
 }