Enable RL sync by default on iOS

components/browser_sync/profile_sync_components_factory_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/browser_sync/profile_sync_components_factory_impl.h"
 
 #include <utility>
 
 #include "base/debug/dump_without_crashing.h"
 #include "base/feature_list.h"
@@ skipping 256 matching lines @@
         base::MakeUnique<UIDataTypeController>(syncer::PRIORITY_PREFERENCES,
                                                error_callback, sync_client_));
   }
 
   // Article sync is disabled by default.  Register only if explicitly enabled.
   if (dom_distiller::IsEnableSyncArticlesSet()) {
     sync_service->RegisterDataTypeController(
         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)) {
+
+#if defined(OS_IOS)

[pavely, 2016/11/20 02:31:58]

Yes, this is a correct way to only enable type on supported platform.
https://cs.chromium.org/chromium/src/chrome/browser/sync/chrome_sync_client.c...

[Olivier, 2016/11/20 10:32:33]

Acknowledged.

+  // Reading list sync is enabled by default only on iOS.  Register unless
+  // explicitly disabled.
+  if (!disabled_types.Has(syncer::READING_LIST)) {
     sync_service->RegisterDataTypeController(
         base::MakeUnique<ModelTypeController>(
             syncer::READING_LIST, error_callback, sync_client_,
             base::ThreadTaskRunnerHandle::Get()));
   }
+#endif
 }
 
 DataTypeManager* ProfileSyncComponentsFactoryImpl::CreateDataTypeManager(
     const syncer::WeakHandle<syncer::DataTypeDebugInfoListener>&
         debug_info_listener,
     const DataTypeController::TypeMap* controllers,
     const syncer::DataTypeEncryptionHandler* encryption_handler,
     syncer::SyncBackendHost* backend,
     DataTypeManagerObserver* observer) {
   return new DataTypeManagerImpl(debug_info_listener, controllers,
@@ skipping 123 matching lines @@
 
 // static
 void ProfileSyncComponentsFactoryImpl::OverridePrefsForUssTest(bool use_uss) {
   override_prefs_controller_to_uss_for_test_ = use_uss;
 }
 
 bool ProfileSyncComponentsFactoryImpl::
     override_prefs_controller_to_uss_for_test_ = false;
 
 }  // namespace browser_sync