Supporting undoing bookmark deletion without creating new ID.

components/bookmarks/browser/bookmark_model.h

Index: components/bookmarks/browser/bookmark_model.h
diff --git a/components/bookmarks/browser/bookmark_model.h b/components/bookmarks/browser/bookmark_model.h
index 27837703d0adc6719ef330fb483cd6afe1d1bcb7..de4690055a3cb830d5f62d0d2fbfc6da9e1a534f 100644
--- a/components/bookmarks/browser/bookmark_model.h
+++ b/components/bookmarks/browser/bookmark_model.h
@@ -308,6 +308,18 @@ class BookmarkModel : public KeyedService {
   // Returns the client used by this BookmarkModel.
   BookmarkClient* client() const { return client_; }
 
+  // Turns on/off the capability to undo removing nodes.
+  void EnableUndoableRemove();

[sky, 2015/10/02 15:40:30]

I think all the bookkeeping of undo should be kept in the undo area. To enable
BookmarkUndoService we should add an interface called BookmarkModelUndoDelegate.
At the appropriate times (remove, insert, change...) BookmarkModel will call
into the BookmarkModelUndoDelegate. 

Why do we need an interface interface? At a minimum this interface is given
ownership of removed nodes. This is unique. No doubt there will be other unique
abilities that need to be given to the BookmarkModelUndoDelegate.

[jianli, 2015/10/06 22:08:24]

Done.

+  void DisableUndoableRemove();
+
+  // Undo deleting the node with |node_id| by putting it back to its original
+  // position.
+  void UndoRemove(int64_t node_id);
+
+  // Throws aways the undo info for the deleted node. After this, the deleted
+  // node can no longer be restored.
+  void DiscardUndoableRemovedNode(int64_t node_id);
+
  private:
   friend class BookmarkCodecTest;
   friend class BookmarkModelFaviconTest;
@@ -323,6 +335,13 @@ class BookmarkModel : public KeyedService {
     }
   };
 
+  // Used to track all the info necessary to bring back a deleted node.
+  struct RestorableDeletedNodeInfo {
+    int64_t parent_node_id;
+    int index;
+    BookmarkNode* node;
+  };
+
   // Implementation of IsBookmarked. Before calling this the caller must obtain
   // a lock on |url_lock_|.
   bool IsBookmarkedNoLock(const GURL& url);
@@ -405,6 +424,9 @@ class BookmarkModel : public KeyedService {
   scoped_ptr<BookmarkLoadDetails> CreateLoadDetails(
       const std::string& accept_languages);
 
+  // Discards all removed nodes that are tracked for restoring.
+  void DiscardAllUndoableRemovedNodes();
+
   BookmarkClient* const client_;
 
   // Whether the initial set of data has been loaded.
@@ -449,6 +471,12 @@ class BookmarkModel : public KeyedService {
 
   std::set<std::string> non_cloned_keys_;
 
+  // Whether or not to support undoing node removal.
+  bool undoable_remove_enabled_;
+
+  // Tracks those deleted nodes that can be restored by the undo operations.
+  std::map<int64_t, RestorableDeletedNodeInfo> undoable_deleted_nodes_;
+
   DISALLOW_COPY_AND_ASSIGN(BookmarkModel);
 };