[MD Bookmarks] Make drag and drop update data model.

chrome/browser/resources/md_bookmarks/dnd_manager.js

 // Copyright 2017 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.
 
 /**
  * Enumeration of valid drop locations relative to an element. These are
  * bit masks to allow combining multiple locations in a single value.
  * @enum {number}
  * @const
  */
@@ skipping 268 matching lines @@
       this.dropIndicator_.finish();
     },
 
     /**
      * @private
      * @param {!Event} e
      */
     onDrop_: function(e) {
       if (this.dropDestination_) {
         e.preventDefault();
+
+        var dropInfo = this.calculateDropInfo_(this.dropDestination_);
+        if (dropInfo.index != -1)
+          chrome.bookmarkManagerPrivate.drop(dropInfo.parentId, dropInfo.index);
+        else
+          chrome.bookmarkManagerPrivate.drop(dropInfo.parentId);
       }
       this.dropDestination_ = null;
       this.dropIndicator_.finish();
     },
 
+    /**
+     * @param {DropDestination} dropDestination
+     * @return {?{parentId: string, index: number}}

[tsergeant, 2017/03/29 00:32:48]

Nit: This shouldn't be nullable, there's no early return here.

[calamity, 2017/03/29 03:35:37]

Done.

+     */
+    calculateDropInfo_: function(dropDestination) {
+      var node = getBookmarkNode(dropDestination.element);
+      var position = dropDestination.position;
+      var parentId = position == DropPosition.ON || !node.parentId ?
+          node.id :
+          node.parentId;
+      var index = -1;
+
+      if (position != DropPosition.ON) {
+        var state = bookmarks.Store.getInstance().data;
+        var listItems = bookmarks.util.getDisplayedList(state);

[tsergeant, 2017/03/29 00:32:48]

I think that since you can't drop onto search results, it is sufficient to do:

index = state.nodes[parentId].children.indexOf(node.id)

This does feel kind of subtle, though, so I'm happy to stick with the current
more explicit version if you prefer.

[calamity, 2017/03/29 03:35:37]

Changed, added a comment.

[tsergeant, 2017/03/29 04:28:01]

I actually meant that you can replace the whole if/else block with that line:
you can see that there's effectively no difference between the two branches in
the latest patchset.

[calamity, 2017/03/30 01:57:54]

Ah yeah, I made this a bit more clear.

+        // TODO(calamity): Handle dropping to an empty bookmark list.
+        if (isBookmarkItem(dropDestination.element)) {
+          index = listItems.indexOf(node.id);
+        } else {
+          index = state.nodes[node.parentId].children.indexOf(node.id);
+        }
+
+        if (position == DropPosition.BELOW)
+          index++;
+      }
+
+      return {
+        index: index,
+        parentId: parentId,
+      };
+    },
+
     /** @private */
     clearDragData_: function() {
       this.dragInfo_.clearDragData();
       this.dropDestination_ = null;
       this.dropIndicator_.finish();
     },
 
     /**
      * @private
      * @param {Event} e
@@ skipping 209 matching lines @@
       return !this.dragInfo_.isDraggingChildBookmark(overElement.itemId)
     },
   };
 
   return {
     DNDManager: DNDManager,
     DragInfo: DragInfo,
     DropIndicator: DropIndicator,
   };
 });