Add methods to Reading List Model

ios/chrome/browser/reading_list/reading_list_model_observer.h

Index: ios/chrome/browser/reading_list/reading_list_model_observer.h
diff --git a/ios/chrome/browser/reading_list/reading_list_model_observer.h b/ios/chrome/browser/reading_list/reading_list_model_observer.h
index e438e36632c42b09d26f060ea286afe14780c47c..1d7bea850fcdda8a8cbaa1a343aed2ed82ebbc84 100644
--- a/ios/chrome/browser/reading_list/reading_list_model_observer.h
+++ b/ios/chrome/browser/reading_list/reading_list_model_observer.h
@@ -40,10 +40,9 @@ class ReadingListModelObserver {
                                                 size_t index) {}
   virtual void ReadingListWillRemoveReadEntry(const ReadingListModel* model,
                                               size_t index) {}
-  // Invoked when elements are moved from unread to read. (The opposite does not
-  // exist as moving an element from read to unread is considered akin to
-  // deleting and re-adding it.) |index| is the original position in the unread
-  // list. The element will be added to the beginning of the read list.
+  // Invoked when elements are moved from unread to read or from read to unread.
+  // |index| is the original position in the origin list. The element will be
+  // added to the beginning of the target list.
   virtual void ReadingListWillMoveEntry(const ReadingListModel* model,
                                         size_t index) {}