Added AddDownload communication path and observers

content/public/browser/background_fetch_client.h

Index: content/public/browser/background_fetch_client.h
diff --git a/content/public/browser/background_fetch_client.h b/content/public/browser/background_fetch_client.h
index 1aad804e99a75da39665dfa15c39279bbc84c773..a77daa455e6394ef680b68099f54e6c211187b4a 100644
--- a/content/public/browser/background_fetch_client.h
+++ b/content/public/browser/background_fetch_client.h
@@ -40,6 +40,12 @@ class CONTENT_EXPORT BackgroundFetchClient {
   // reset the delegate back to a `nullptr` when it's being destructed.
   virtual void SetDelegate(Delegate* delegate) = 0;
 
+  // Notify the client that a Background Fetch download has started, including
+  // all information needed to display a notification of the download.
+  virtual void AddDownload(const std::string& registration_id,
+                           const std::string& title,
+                           int64_t total_download_size) = 0;
+
  protected:
   virtual ~BackgroundFetchClient() {}
 };