Reading List: Mark entry read when opening external app.

ios/chrome/browser/reading_list/reading_list_web_state_observer.h

Index: ios/chrome/browser/reading_list/reading_list_web_state_observer.h
diff --git a/ios/chrome/browser/reading_list/reading_list_web_state_observer.h b/ios/chrome/browser/reading_list/reading_list_web_state_observer.h
index 349bdc0a64d4ee7c9e0e8f9016e6be825894f450..170b27b4e958eaf5f5fb6ab1daa4dae4c51376ad 100644
--- a/ios/chrome/browser/reading_list/reading_list_web_state_observer.h
+++ b/ios/chrome/browser/reading_list/reading_list_web_state_observer.h
@@ -33,6 +33,10 @@ class ReadingListWebStateObserver : public web::WebStateObserver,
   void ReadingListModelLoaded(const ReadingListModel* model) override;
   void ReadingListModelBeingDeleted(const ReadingListModel* model) override;
 
+  // Notify the observer that current navigation triggered an external app and
+  // that the entry should be considered as read.
+  void CurrentNavigationWillContinueInExternalApp();
+
  private:
   ReadingListWebStateObserver(web::WebState* web_state,
                               ReadingListModel* reading_list_model);