[MD-Settings-A11y] cr-expand-button should communicate that it expanded.

chrome/test/data/chromeos/oobe_webui_browsertest.js

Index: chrome/test/data/chromeos/oobe_webui_browsertest.js
diff --git a/chrome/test/data/chromeos/oobe_webui_browsertest.js b/chrome/test/data/chromeos/oobe_webui_browsertest.js
index c14bff61175406419b109021fba17c70f2f2ca92..34f3f9b5b6a7445a21821f95125d2922698e9e30 100644
--- a/chrome/test/data/chromeos/oobe_webui_browsertest.js
+++ b/chrome/test/data/chromeos/oobe_webui_browsertest.js
@@ -77,6 +77,12 @@ OobeWebUITest.prototype = {
       'requiredOwnedAriaRoleMissing',
       requiredOwnedAriaRoleMissingSelectors);
 
+    // Polymer.PaperButtonBehavior.ariaActiveAttribute starts with aria- but is
+    // not an ARIA attribute. Ignore for paper-icon-button.
+    this.accessibilityAuditConfig.ignoreSelectors(
+      'badAriaAttribute',
+      'paper-icon-button[aria-active-attribute]');
+
     var badAriaAttributeSelectors = [
       '#forgotPasswordDlg',
       '#cancelConfirmDlg',