Offline Pages: Replace Observer::OfflinePageModelChanged with OfflinePageAdded.

components/offline_pages/offline_page_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 "components/offline_pages/offline_page_model.h"
 
 #include "url/gurl.h"
 
 namespace offline_pages {
+using Observer = OfflinePageModel::Observer;
+
+// Invoked when the model has finished loading.
+void Observer::OfflinePageModelLoaded(OfflinePageModel* model) {}
+
+// Invoked when the model is being updated due to adding an offline page.
+void Observer::OfflinePageAdded(OfflinePageModel* model,
+                                SavePageResult result,
+                                const OfflinePageItem* added) {}
+
+// Invoked when an offline copy related to |offline_id| was deleted.
+void Observer::OfflinePageDeleted(int64_t offline_id,
+                                  const ClientId& client_id) {}
+
+Observer::~Observer() = default;
 
 // static
 bool OfflinePageModel::CanSaveURL(const GURL& url) {
   return url.is_valid() && url.SchemeIsHTTPOrHTTPS();
 }
 
 OfflinePageModel::OfflinePageModel() {}
 
 OfflinePageModel::~OfflinePageModel() {}
 
 }  // namespace offline_pages