Eliminate Bookmarks dependence to bookmark_undo_utils.h.

chrome/browser/bookmarks/bookmark_model_observer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_BOOKMARKS_BOOKMARK_MODEL_OBSERVER_H_
 #define CHROME_BROWSER_BOOKMARKS_BOOKMARK_MODEL_OBSERVER_H_
 
 class BookmarkModel;
 class BookmarkNode;
 
@@ skipping 81 matching lines @@
   // This tells observers to update themselves if they were waiting for the
   // update to finish.
   virtual void ExtensiveBookmarkChangesEnded(BookmarkModel* model) {}
 
   // Invoked before all non-permanent bookmark nodes are removed.
   virtual void OnWillRemoveAllBookmarks(BookmarkModel* model) {}
 
   // Invoked when all non-permanent bookmark nodes have been removed.
   virtual void BookmarkAllNodesRemoved(BookmarkModel* model) = 0;
 
+  // Invoked before a set of model changes initiated by a single user action
+  // is about to begin.

[sky, 2014/02/06 17:48:27]

Give an example of what this entails, and one comment for the two should
suffice.

[Tom Cassiotis, 2014/02/21 17:51:45]

Done.

+  virtual void GroupedBookmarkChangesBeginning(BookmarkModel* model) {}
+
+  // Invoked after a set of model changes triggered by a single user action has
+  // ended.
+  virtual void GroupedBookmarkChangesEnded(BookmarkModel* model) {}
+
  protected:
   virtual ~BookmarkModelObserver() {}
 };
 
 #endif  // CHROME_BROWSER_BOOKMARKS_BOOKMARK_MODEL_OBSERVER_H_