Enable RL sync by default on iOS

components/reading_list/proto/reading_list.proto

-// Copyright 2016 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.
-//
-// Sync protocol datatype extension for the reading list items.
-
-syntax = "proto2";
-
-option optimize_for = LITE_RUNTIME;
-
-package reading_list;
-
-// Local Reading list entry. This proto contains the fields stored locally for
-// a reading list entry. It must be kept synced with the
-// sync_pb.ReadingListSpecifics protobuf.
-message ReadingListLocal {
-  optional string entry_id = 1;
-
-  optional string title = 2;
-
-  optional string url = 3;
-
-  optional int64 creation_time_us = 4;
-
-  optional int64 update_time_us = 5;
-
-  enum ReadingListEntryStatus {
-    UNREAD = 0;
-    READ = 1;
-  }
-
-  optional ReadingListEntryStatus status = 6;
-
-  enum DistillationState {
-    WAITING = 0;
-    PROCESSING = 1;
-    PROCESSED = 2;
-    WILL_RETRY = 3;
-    ERROR = 4;
-  }
-  optional DistillationState distillation_state = 7;
-  optional string distilled_path = 8;
-  optional int64 failed_download_counter = 9;
-  optional string backoff = 10;
-}