[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 265 matching lines @@
     /** @private */
     onDragLeave_: function() {
       this.dropIndicator_.finish();
     },
 
     /**
      * @private
      * @param {!Event} e
      */
     onDrop_: function(e) {
-      if (this.dropDestination_)
+      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}}
+     */
+    calculateDropInfo_: function(dropDestination) {
+      var node = getBookmarkNode(dropDestination.element);
+      var position = dropDestination.position;
+      var index = -1;
+      var parentId = node.id;
+
+      if (position != DropPosition.ON) {
+        var state = bookmarks.Store.getInstance().data;
+
+        // Drops between items in the normal list and the sidebar use the drop
+        // destination node's parent.
+        parentId = node.parentId || '';

[tsergeant, 2017/03/30 04:02:15]

Nit: Maybe assert(node.parentId) here, instead of defaulting to the empty
string.

The end result is the same (since the empty string will just error on the line
below), but the behavior is slightly nicer.

[calamity, 2017/04/03 03:02:28]

Done.

+        index = state.nodes[parentId].children.indexOf(node.id);
+
+        // TODO(calamity): Handle dropping to an empty bookmark list.
+        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 207 matching lines @@
       return !this.dragInfo_.isDraggingChildBookmark(overElement.itemId)
     },
   };
 
   return {
     DNDManager: DNDManager,
     DragInfo: DragInfo,
     DropIndicator: DropIndicator,
   };
 });