Move ReadingList model to components/reading_list/core

components/reading_list/core/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;
 
@@ skipping 17 matching lines @@
     UNSEEN = 2;
   }
   // If the field is not present, it defaults to UNSEEN.
   optional ReadingListEntryStatus status = 6;
 
   enum DistillationState {
     WAITING = 0;
     PROCESSING = 1;
     PROCESSED = 2;
     WILL_RETRY = 3;
-    ERROR = 4;
+    DISTILLATION_ERROR = 4;
   }
   optional DistillationState distillation_state = 7;
   optional string distilled_path = 8;
   optional string distilled_url = 13;
   optional int64 failed_download_counter = 9;
   optional string backoff = 10;
   optional int64 distillation_time_us = 14;
   optional int64 distillation_size = 15;
 }