[Offline Pages] Add cached offline page utils and show usage in settings.

components/offline_pages/core/offline_page_types.h

Index: components/offline_pages/core/offline_page_types.h
diff --git a/components/offline_pages/core/offline_page_types.h b/components/offline_pages/core/offline_page_types.h
index 4bb3342e1d1daf79d0db433ff349f528e98624fc..e266bba419b763562c5fda04008f09b11b58e6f0 100644
--- a/components/offline_pages/core/offline_page_types.h
+++ b/components/offline_pages/core/offline_page_types.h
@@ -77,6 +77,7 @@ typedef base::Callback<void(const OfflinePageItem*)>
 typedef base::Callback<void(const MultipleOfflinePageItemResult&)>
     MultipleOfflinePageItemCallback;
 typedef base::Callback<bool(const GURL&)> UrlPredicate;
+typedef base::Callback<void(int64_t)> SizeInBytesCallback;
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_OFFLINE_PAGE_TYPES_H_