MD Bookmarks: Show toolbar overlay when multiple items are selected

chrome/test/data/webui/md_bookmarks/toolbar_test.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.
+
+suite('<bookmarks-toolbar>', function() {
+  var toolbar;
+  var store;
+
+  setup(function() {
+    store = new bookmarks.TestStore({
+      nodes: testTree(createFolder('1', [
+        createItem('2'),
+        createItem('3'),
+      ])),
+      selection: {
+        items: new Set(),
+        anchor: null,
+      },
+    });
+    bookmarks.Store.instance_ = store;
+
+    toolbar = document.createElement('bookmarks-toolbar');
+    replaceBody(toolbar);
+  });
+
+  test('selecting multiple items shows toolbar overlay', function() {
+    assertFalse(toolbar.showSelectionOverlay);
+
+    store.data.selection.items = new Set(['2']);
+    store.notifyObservers();
+    assertFalse(toolbar.showSelectionOverlay);
+
+    store.data.selection.items = new Set(['2', '3']);
+    store.notifyObservers();
+    assertTrue(toolbar.showSelectionOverlay);
+  });
+});