[MD Bookmarks] Add keyboard navigation and selection to bookmark list.

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.
  */
@@ skipping 47 matching lines @@
   SelectionState.deselectDeletedItems = function(selectionState, deleted) {
     return /** @type {SelectionState} */ Object.assign({}, selectionState, {
       items: bookmarks.util.removeIdsFromSet(selectionState.items, deleted),
       anchor: !selectionState.anchor || deleted.has(selectionState.anchor) ?
           null :
           selectionState.anchor,
     });
   };
 
   /**
+   * @param {SelectionState} selectionState
+   * @param {Action} action
+   * @return {SelectionState}
+   */
+  SelectionState.updateAnchor = function(selectionState, action) {
+    return /** @type {SelectionState} */ (Object.assign({}, selectionState, {
+      anchor: action.anchor,
+    }));
+  };
+
+  /**
    * @param {SelectionState} selection
    * @param {Action} action
    * @return {SelectionState}
    */
   SelectionState.updateSelection = function(selection, action) {
     switch (action.name) {
       case 'clear-search':
       case 'finish-search':
       case 'select-folder':
       case 'deselect-items':
         return SelectionState.deselectAll(selection);
       case 'select-items':
         return SelectionState.selectItems(selection, action);
       case 'remove-bookmark':
         return SelectionState.deselectDeletedItems(
             selection, action.descendants);
+      case 'update-anchor':
+        return SelectionState.updateAnchor(selection, action);
       default:
         return selection;
     }
   };
 
   var SearchState = {};
 
   /**
    * @param {SearchState} search
    * @param {Action} action
@@ skipping 337 matching lines @@
 
   return {
     reduceAction: reduceAction,
     ClosedFolderState: ClosedFolderState,
     NodeState: NodeState,
     SearchState: SearchState,
     SelectedFolderState: SelectedFolderState,
     SelectionState: SelectionState,
   };
 });