[Win10 FRE] Fix ARIA attributes to conform to accordion widget.

chrome/browser/resources/welcome/win10/inline.js

Index: chrome/browser/resources/welcome/win10/inline.js
diff --git a/chrome/browser/resources/welcome/win10/inline.js b/chrome/browser/resources/welcome/win10/inline.js
index a4530a673714c64f767dd37539d30dbd6fa36092..bef49ae4d76961e3e1cfb4ee2c48257d13613672 100644
--- a/chrome/browser/resources/welcome/win10/inline.js
+++ b/chrome/browser/resources/welcome/win10/inline.js
@@ -47,11 +47,13 @@ Polymer({
   },
 
   onToggle: function() {
-    if (this.isCombined) {
-      var sections = this.shadowRoot.querySelectorAll('.section.expandable');
-      sections.forEach(function(section) {
-        section.classList.toggle('expanded');
-      });
-    }
+    if (!this.isCombined)
+      return;
+    var sections = this.shadowRoot.querySelectorAll('.section.expandable');
+    sections.forEach(function(section) {
+      var isExpanded = section.classList.toggle('expanded');
+      section.querySelector('[role~="button"]').setAttribute(
+          'aria-expanded', isExpanded);
+    });
   }
 });