Add Store+Sync to reading list.

ios/chrome/browser/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 sync_pb;
+package reading_list;
 
-// Properties of Reading list items.
-message ReadingListSpecifics {
+// Local Reading list entry.
+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_url = 8;
+  optional string backoff = 9;
 }