[MD Bookmarks] Add undo/redo functionality to MD Bookmarks.

chrome/browser/bookmarks/bookmark_model_factory.cc

Index: chrome/browser/bookmarks/bookmark_model_factory.cc
diff --git a/chrome/browser/bookmarks/bookmark_model_factory.cc b/chrome/browser/bookmarks/bookmark_model_factory.cc
index 46069a63f171a5c6647cf839d8682b6dfe99ae56..dff7105519351aa336838b6fbcf099a0ad1188e4 100644
--- a/chrome/browser/bookmarks/bookmark_model_factory.cc
+++ b/chrome/browser/bookmarks/bookmark_model_factory.cc
@@ -15,6 +15,7 @@
 #include "chrome/browser/bookmarks/startup_task_runner_service_factory.h"
 #include "chrome/browser/profiles/incognito_helpers.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/webui/md_bookmarks/md_bookmarks_ui.h"
 #include "chrome/browser/undo/bookmark_undo_service_factory.h"
 #include "chrome/common/chrome_switches.h"
 #include "components/bookmarks/browser/bookmark_model.h"
@@ -73,7 +74,8 @@ KeyedService* BookmarkModelFactory::BuildServiceInstanceFor(
 #if !defined(OS_ANDROID)
   register_bookmark_undo_service_as_observer =
       base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kEnableBookmarkUndo);
+          switches::kEnableBookmarkUndo) ||
+      MdBookmarksUI::IsEnabled();
 #endif  // !defined(OS_ANDROID)
   if (register_bookmark_undo_service_as_observer)
     BookmarkUndoServiceFactory::GetForProfile(profile)->Start(bookmark_model);