Offline Pages: Replace Observer::OfflinePageModelChanged with OfflinePageAdded.

components/offline_pages/offline_page_model.cc

Index: components/offline_pages/offline_page_model.cc
diff --git a/components/offline_pages/offline_page_model.cc b/components/offline_pages/offline_page_model.cc
index cd0a93705f20b8ed1807c2f807e2a1641a37f4f7..7c005017f91ce6c4a9d5f467218e053136956af3 100644
--- a/components/offline_pages/offline_page_model.cc
+++ b/components/offline_pages/offline_page_model.cc
@@ -7,6 +7,21 @@
 #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) {