Add Store+Sync to reading list.

ios/chrome/browser/reading_list/reading_list_model_factory.h

Index: ios/chrome/browser/reading_list/reading_list_model_factory.h
diff --git a/ios/chrome/browser/reading_list/reading_list_model_factory.h b/ios/chrome/browser/reading_list/reading_list_model_factory.h
index 6d18ef1ca01e4dcc05c621e8a41da76ac7683fea..3c5e9601c9d0cb4696886e1e7a5070abe2a068f5 100644
--- a/ios/chrome/browser/reading_list/reading_list_model_factory.h
+++ b/ios/chrome/browser/reading_list/reading_list_model_factory.h
@@ -15,6 +15,7 @@ struct DefaultSingletonTraits;
 }  // namespace base
 
 class ReadingListModel;
+class ReadingListStore;
 
 namespace ios {
 class ChromeBrowserState;
@@ -24,6 +25,8 @@ class ChromeBrowserState;
 // ios::ChromeBrowserState.
 class ReadingListModelFactory : public BrowserStateKeyedServiceFactory {
  public:
+  // Returns if Reading List is enabled on this device.
+  static bool IsReadingListEnabled();
   static ReadingListModel* GetForBrowserState(
       ios::ChromeBrowserState* browser_state);
   static ReadingListModel* GetForBrowserStateIfExists(