Enable RL sync by default on iOS

components/browser_sync/profile_sync_components_factory_impl.cc

Index: components/browser_sync/profile_sync_components_factory_impl.cc
diff --git a/components/browser_sync/profile_sync_components_factory_impl.cc b/components/browser_sync/profile_sync_components_factory_impl.cc
index c4332e02bdc969cd0fa5b05a11bd7e5b61822f33..eae3dc111afd748975884e8723bf140fece6bf89 100644
--- a/components/browser_sync/profile_sync_components_factory_impl.cc
+++ b/components/browser_sync/profile_sync_components_factory_impl.cc
@@ -26,6 +26,7 @@
 #include "components/password_manager/core/browser/password_store.h"
 #include "components/password_manager/sync/browser/password_data_type_controller.h"
 #include "components/prefs/pref_service.h"
+#include "components/reading_list/core/reading_list_switches.h"
 #include "components/sync/base/report_unrecoverable_error.h"
 #include "components/sync/device_info/device_info_data_type_controller.h"
 #include "components/sync/device_info/local_device_info_provider_impl.h"
@@ -274,9 +275,11 @@ void ProfileSyncComponentsFactoryImpl::RegisterCommonDataTypes(
         base::MakeUnique<UIDataTypeController>(syncer::ARTICLES, error_callback,
                                                sync_client_));
   }
-  // Reading list sync is disabled by default.  Register only if explicitly
-  // enabled.
-  if (enabled_types.Has(syncer::READING_LIST)) {
+
+  // Reading list sync is enabled by default only on iOS. Register unless
+  // Reading List or Reading List Sync is explicitly disabled.
+  if (!disabled_types.Has(syncer::READING_LIST) &&
+      reading_list::switches::IsReadingListEnabled()) {
     sync_service->RegisterDataTypeController(
         base::MakeUnique<ModelTypeController>(
             syncer::READING_LIST, error_callback, sync_client_,