[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();

[sky, 2017/05/24 16:57:16]

Where do we make use of the undo in non-android? For example,
chrome/browser/ui/bookmarks/bookmark_context_menu_controller.cc doesn't look at
this conditional. How about a single function for testing if undo is enabled so
it's easier to update all places?

[calamity, 2017/05/25 08:54:02]

It's behind a flag for the bookmarks bar context menu, but that's all I think.
I've made the BookmarkUndoService::IsEnabled() function but I don't think I
should hook the Bookmarks Bar context menu up to that function because it's a
product change and should probably go through a PM/UX once-over first.

I think we'll aim to remove the kEnableBookmarkUndo flag one way or the other.
We'll either enable it for the context menu always, or remove the context menu
code and have it locked to MD Bookmarks.

[sky, 2017/05/25 18:09:06]

If you don't enable undo in the menu how is it possible to use undo?

Given your in a different timezone I'm going to approve this assuming you have
it wired up somewhere.

 #endif  // !defined(OS_ANDROID)
   if (register_bookmark_undo_service_as_observer)
     BookmarkUndoServiceFactory::GetForProfile(profile)->Start(bookmark_model);