Add methods to Reading List Model

ios/chrome/browser/reading_list/reading_list_model.h

Index: ios/chrome/browser/reading_list/reading_list_model.h
diff --git a/ios/chrome/browser/reading_list/reading_list_model.h b/ios/chrome/browser/reading_list/reading_list_model.h
index 40b3551e857969734016763869ee7e7e72f20073..052bbe1ce47a3f5fa18a30106c15f904d0306d60 100644
--- a/ios/chrome/browser/reading_list/reading_list_model.h
+++ b/ios/chrome/browser/reading_list/reading_list_model.h
@@ -79,6 +79,10 @@ class ReadingListModel {
   // the reading list and read, move it to the top of unread if it is not here
   // already. This may trigger deletion of old read entries.
   virtual void MarkReadByURL(const GURL& url) = 0;
+  // If the |url| is in the reading list and read, mark it unread. If it is in
+  // the reading list and unread, move it to the top of read if it is not here
+  // already.
+  virtual void MarkUnreadByURL(const GURL& url) = 0;
 
   // Methods to mutate an entry. Will locate the relevant entry by URL. Does
   // nothing if the entry is not found.