Added AddDownload communication path and observers

chrome/browser/background_fetch/background_fetch_client_impl.h

Index: chrome/browser/background_fetch/background_fetch_client_impl.h
diff --git a/chrome/browser/background_fetch/background_fetch_client_impl.h b/chrome/browser/background_fetch/background_fetch_client_impl.h
index c812d126ba2fc11d3a13be3b2b25f00b8d371424..d2f08f03f037b24f0cbed1cf976f43eb70f6c683 100644
--- a/chrome/browser/background_fetch/background_fetch_client_impl.h
+++ b/chrome/browser/background_fetch/background_fetch_client_impl.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/offline_items_collection/core/offline_content_provider.h"
 #include "content/public/browser/background_fetch_client.h"
@@ -32,6 +33,9 @@ class BackgroundFetchClientImpl
 
   // content::BackgroundFetchClient implementation.
   void SetDelegate(content::BackgroundFetchClient::Delegate* delegate) override;
+  void AddDownload(const std::string& registration_id,
+                   const std::string& title,
+                   int64_t total_download_size) override;
 
   // components::offline_items_collection::OfflineContentProvider overrides.
   bool AreItemsAvailable() override;
@@ -59,11 +63,14 @@ class BackgroundFetchClientImpl
 
   // The |delegate| is owned externally and will remove itself prior to
   // deletion.
-  content::BackgroundFetchClient::Delegate* delegate_;
+  content::BackgroundFetchClient::Delegate* delegate_ = nullptr;
 
   // The name of the namespace registered with the aggregator.
   std::string namespace_;
 
+  // A list of all currently registered observers.
+  base::ObserverList<OfflineContentProvider::Observer> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(BackgroundFetchClientImpl);
 };