[MD Bookmarks] Refine mouse selection

chrome/browser/resources/md_bookmarks/reducers.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.
 
 /**
  * @fileoverview Module of functions which produce a new page state in response
  * to an action. Reducers (in the same sense as Array.prototype.reduce) must be
  * pure functions: they must not modify existing state objects, or make any API
  * calls.
  */
 
 cr.define('bookmarks', function() {
   var SelectionState = {};
 
   /**
    * @param {SelectionState} selectionState
    * @param {Action} action
    * @return {SelectionState}
    */
   SelectionState.selectItems = function(selectionState, action) {
     var newItems = new Set();
-    if (action.add)
+    if (!action.clear)
       newItems = new Set(selectionState.items);
 
     action.items.forEach(function(id) {
-      newItems.add(id);
+      var add = true;
+      if (action.toggle)
+        add = !newItems.has(id);
+
+      if (add)
+        newItems.add(id);
+      else
+        newItems.delete(id);
     });
 
     return /** @type {SelectionState} */ (Object.assign({}, selectionState, {
       items: newItems,
       anchor: action.anchor,
     }));
   };
 
   /**
    * @param {SelectionState} selectionState
    * @return {SelectionState}
    */
   SelectionState.deselectAll = function(selectionState) {
     return {
       items: new Set(),
       anchor: null,
     };
   };
 
   /**
    * @param {SelectionState} selectionState
    * @param {!Set<string>} deleted
    * @return SelectionState
    */
   SelectionState.deselectDeletedItems = function(selectionState, deleted) {
     return /** @type {SelectionState} */ Object.assign({}, selectionState, {
       items: bookmarks.util.removeIdsFromSet(selectionState.items, deleted),
-      anchor: null,
+      anchor: !selectionState.anchor || deleted.has(selectionState.anchor) ?
+          null :
+          selectionState.anchor,
     });
   };
 
   /**
    * @param {SelectionState} selection
    * @param {Action} action
    * @return {SelectionState}
    */
   SelectionState.updateSelection = function(selection, action) {
     switch (action.name) {
@@ skipping 357 matching lines @@
 
   return {
     reduceAction: reduceAction,
     ClosedFolderState: ClosedFolderState,
     NodeState: NodeState,
     SearchState: SearchState,
     SelectedFolderState: SelectedFolderState,
     SelectionState: SelectionState,
   };
 });