[Offline pages] Resetting offline page metadata store to handle LOAD/INIT failures

components/offline_pages/offline_page_metadata_store.h

Index: components/offline_pages/offline_page_metadata_store.h
diff --git a/components/offline_pages/offline_page_metadata_store.h b/components/offline_pages/offline_page_metadata_store.h
index 26314804bdce08b2df6e0ad0280aee4937a3fb73..8e0e656ef73c67559b8735d23a8bdb7f705ea3dc 100644
--- a/components/offline_pages/offline_page_metadata_store.h
+++ b/components/offline_pages/offline_page_metadata_store.h
@@ -38,8 +38,9 @@ class OfflinePageMetadataStore {
     LOAD_STATUS_COUNT
   };
 
-  typedef base::Callback<void(LoadStatus, const std::vector<OfflinePageItem>&)>
+  typedef base::Callback<void(const std::vector<OfflinePageItem>&)>
       LoadCallback;
+  typedef base::Callback<void(bool)> InitializeCallback;
   typedef base::Callback<void(ItemActionStatus)> AddCallback;
   typedef base::Callback<void(std::unique_ptr<OfflinePagesUpdateResult>)>
       UpdateCallback;
@@ -48,6 +49,9 @@ class OfflinePageMetadataStore {
   OfflinePageMetadataStore();
   virtual ~OfflinePageMetadataStore();
 
+  // Initializes the store. Should be called before any other methods.
+  virtual void Initialize(const InitializeCallback& callback) = 0;
+
   // Get all of the offline pages from the store.
   virtual void GetOfflinePages(const LoadCallback& callback) = 0;