Have the RequestCoordinator generate the offline_id

components/offline_pages/offline_page_model_impl.h

 // 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.
 
 #ifndef COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_IMPL_H_
 #define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 50 matching lines @@
       std::unique_ptr<OfflinePageMetadataStore> store,
       const base::FilePath& archives_dir,
       const scoped_refptr<base::SequencedTaskRunner>& task_runner);
   ~OfflinePageModelImpl() override;
 
   // Implemented methods:
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
   void SavePage(const GURL& url,
                 const ClientId& client_id,
+                int64_t proposed_offline_id,
                 std::unique_ptr<OfflinePageArchiver> archiver,
                 const SavePageCallback& callback) override;
   void MarkPageAccessed(int64_t offline_id) override;
   void ClearAll(const base::Closure& callback) override;
   void DeletePagesByOfflineId(const std::vector<int64_t>& offline_ids,
                               const DeletePageCallback& callback) override;
   void DeletePagesByURLPredicate(const UrlPredicate& predicate,
                                  const DeletePageCallback& callback) override;
   void HasPages(const std::string& name_space,
                 const HasPagesCallback& callback) override;
@@ skipping 215 matching lines @@
   OfflinePageModelEventLogger offline_event_logger_;
 
   base::WeakPtrFactory<OfflinePageModelImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OfflinePageModelImpl);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_IMPL_H_