[MD Bookmarks] Make dragging update selected items.

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.
 
 cr.define('bookmarks', function() {
   /**
    * @param {BookmarkElement} element
    * @return {boolean}
    */
   function isBookmarkItem(element) {
@@ skipping 353 matching lines @@
       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 = assert(node.parentId);
         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,
       };
     },
 
@@ skipping 11 matching lines @@
 
     /**
      * @private
      * @param {Event} e
      */
     onDragStart_: function(e) {
       var dragElement = getBookmarkElement(e.path);
       if (!dragElement)
         return;
 
+      var store = bookmarks.Store.getInstance();
+      var dragId = dragElement.itemId;
+
       // Determine the selected bookmarks.
-      var state = bookmarks.Store.getInstance().data;
+      var state = store.data;
       var draggedNodes = Array.from(state.selection.items);
 
+      // Change selection to the dragged node if the node is not part of the
+      // existing selection.
       if (isBookmarkFolderNode(dragElement) ||
-          draggedNodes.indexOf(dragElement.itemId) == -1) {
-        // TODO(calamity): clear current selection.
-        draggedNodes = [dragElement.itemId];
+          draggedNodes.indexOf(dragId) == -1) {
+        store.dispatch(bookmarks.actions.deselectItems());
+        if (!isBookmarkFolderNode(dragElement)) {
+          store.dispatch(
+              bookmarks.actions.selectItem(dragId, true, false, state));
+        }
+        draggedNodes = [dragId];
       }
 
       e.preventDefault();
 
       // If we are dragging a single link, we can do the *Link* effect.
       // Otherwise, we only allow copy and move.
       if (e.dataTransfer) {
         e.dataTransfer.effectAllowed =
             draggedNodes.length == 1 && state.nodes[draggedNodes[0]].url ?
             'copyLink' :
@@ skipping 203 matching lines @@
       this.dropIndicator_.setTimeout = this.setTimeout_;
     }
   };
 
   return {
     DNDManager: DNDManager,
     DragInfo: DragInfo,
     DropIndicator: DropIndicator,
   };
 });