MD Bookmarks: Initial screenreader accessibility improvements

chrome/test/data/webui/md_bookmarks/toast_manager_test.js

Index: chrome/test/data/webui/md_bookmarks/toast_manager_test.js
diff --git a/chrome/test/data/webui/md_bookmarks/toast_manager_test.js b/chrome/test/data/webui/md_bookmarks/toast_manager_test.js
index 24ba4218c42f0e68495c6d78069f87544a425295..b7d4dffd24aff09372a9fc5fa3e0c27005d204cd 100644
--- a/chrome/test/data/webui/md_bookmarks/toast_manager_test.js
+++ b/chrome/test/data/webui/md_bookmarks/toast_manager_test.js
@@ -22,6 +22,9 @@ suite('<bookmarks-toast-manager>', function() {
 
     toastManager.show('test', true);
     assertFalse(toastManager.$$('paper-button').hidden);
+
+    toastManager.hide();
+    assertTrue(toastManager.$.button.hidden);
   });
 
   test('auto hide', function() {