Revert of Add Store+Sync to reading list.

ios/chrome/browser/reading_list/reading_list_model.cc

 // 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.
 
 #include "ios/chrome/browser/reading_list/reading_list_model.h"
 
-#include "base/logging.h"
-#include "base/memory/ptr_util.h"
-
 ReadingListModel::ReadingListModel() : current_batch_updates_count_(0) {}
-
 ReadingListModel::~ReadingListModel() {
   for (auto& observer : observers_) {
     observer.ReadingListModelBeingDeleted(this);
   }
 }
 
 // Observer methods.
 void ReadingListModel::AddObserver(ReadingListModelObserver* observer) {
-  DCHECK(CalledOnValidThread());
   DCHECK(observer);
   observers_.AddObserver(observer);
   if (loaded()) {
     observer->ReadingListModelLoaded(this);
   }
 }
 
 void ReadingListModel::RemoveObserver(ReadingListModelObserver* observer) {
-  DCHECK(CalledOnValidThread());
   observers_.RemoveObserver(observer);
 }
 
 // Batch update methods.
 bool ReadingListModel::IsPerformingBatchUpdates() const {
-  DCHECK(CalledOnValidThread());
   return current_batch_updates_count_ > 0;
 }
 
 std::unique_ptr<ReadingListModel::ScopedReadingListBatchUpdate>
-ReadingListModel::CreateBatchToken() {
-  return base::MakeUnique<ReadingListModel::ScopedReadingListBatchUpdate>(this);
-}
-
-std::unique_ptr<ReadingListModel::ScopedReadingListBatchUpdate>
 ReadingListModel::BeginBatchUpdates() {
-  DCHECK(CalledOnValidThread());
-  auto token = CreateBatchToken();
+  std::unique_ptr<ReadingListModel::ScopedReadingListBatchUpdate> token(
+      new ReadingListModel::ScopedReadingListBatchUpdate(this));
 
   ++current_batch_updates_count_;
   if (current_batch_updates_count_ == 1) {
-    EnteringBatchUpdates();
+    for (auto& observer : observers_)
+      observer.ReadingListModelBeganBatchUpdates(this);
   }
   return token;
 }
 
-void ReadingListModel::EnteringBatchUpdates() {
-  DCHECK(CalledOnValidThread());
-  for (auto& observer : observers_)
-    observer.ReadingListModelBeganBatchUpdates(this);
-}
-
 void ReadingListModel::EndBatchUpdates() {
-  DCHECK(CalledOnValidThread());
   DCHECK(IsPerformingBatchUpdates());
-  DCHECK(current_batch_updates_count_ > 0);
   --current_batch_updates_count_;
   if (current_batch_updates_count_ == 0) {
-    LeavingBatchUpdates();
+    for (auto& observer : observers_)
+      observer.ReadingListModelCompletedBatchUpdates(this);
   }
 }
-
-void ReadingListModel::LeavingBatchUpdates() {
-  DCHECK(CalledOnValidThread());
-  for (auto& observer : observers_)
-    observer.ReadingListModelCompletedBatchUpdates(this);
-}
-
-ReadingListModel::ScopedReadingListBatchUpdate::
-    ~ScopedReadingListBatchUpdate() {
-  model_->EndBatchUpdates();
-}