[MD Bookmarks] Change selection items from Map to Set.

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 = {};
+    var newItems = new Set();
     if (action.add)
-      Object.assign(newItems, selectionState.items);
+      newItems = new Set(selectionState.items);
 
     action.items.forEach(function(id) {
-      newItems[id] = true;
+      newItems.add(id);
     });
 
     return /** @type {SelectionState} */ (Object.assign({}, selectionState, {
       items: newItems,
       anchor: action.anchor,
     }));
   };
 
   /**
    * @param {SelectionState} selectionState
    * @return {SelectionState}
    */
   SelectionState.deselectAll = function(selectionState) {
     return {
-      items: {},
+      items: new Set(),
       anchor: null,
     };
   };
 
   /**
    * @param {SelectionState} selection
    * @param {Action} action
    * @return {SelectionState}
    */
   SelectionState.updateSelection = function(selection, action) {
@@ skipping 215 matching lines @@
   var ClosedFolderState = {};
 
   /**
    * @param {ClosedFolderState} closedFolders
    * @param {string|undefined} id
    * @param {NodeList} nodes
    * @return {ClosedFolderState}
    */
   ClosedFolderState.openFolderAndAncestors = function(
       closedFolders, id, nodes) {
-    var modifications = {};
+    var newClosedFolders = new Set(closedFolders);
     var currentId = id;
     while (currentId) {
-      if (closedFolders[currentId])
-        modifications[currentId] = false;
+      if (closedFolders.has(currentId))
+        newClosedFolders.delete(currentId);
 
       currentId = nodes[currentId].parentId;
     }
 
-    return Object.assign({}, closedFolders, modifications);
+    return newClosedFolders;
   };
 
   /**
    * @param {ClosedFolderState} closedFolders
    * @param {Action} action
    * @return {ClosedFolderState}
    */
   ClosedFolderState.changeFolderOpen = function(closedFolders, action) {
     var closed = !action.open;
-    var modification = {};
-    modification[action.id] = closed;
+    var newClosedFolders = new Set(closedFolders);
+    if (closed)
+      newClosedFolders.add(action.id);
+    else
+      newClosedFolders.delete(action.id);
 
-    return Object.assign({}, closedFolders, modification);
+    return newClosedFolders;
   };
 
   /**
    * @param {ClosedFolderState} closedFolders
    * @param {Action} action
    * @param {NodeList} nodes
    * @return {ClosedFolderState}
    */
   ClosedFolderState.updateClosedFolders = function(
       closedFolders, action, nodes) {
@@ skipping 35 matching lines @@
 
   return {
     reduceAction: reduceAction,
     ClosedFolderState: ClosedFolderState,
     NodeState: NodeState,
     SearchState: SearchState,
     SelectedFolderState: SelectedFolderState,
     SelectionState: SelectionState,
   };
 });