arc: Make ChromeVox read an ARC custom notification

ui/message_center/notification.h

Index: ui/message_center/notification.h
diff --git a/ui/message_center/notification.h b/ui/message_center/notification.h
index 579c2be36bc3566a463badfdc477d48fcb40b5e3..93d255e56daa8439201c0348146a3df69e15ee7c 100644
--- a/ui/message_center/notification.h
+++ b/ui/message_center/notification.h
@@ -61,6 +61,7 @@ class MESSAGE_CENTER_EXPORT RichNotificationData {
   std::vector<int> vibration_pattern;
   bool renotify;
   bool silent;
+  base::string16 accessible_name;
 };
 
 class MESSAGE_CENTER_EXPORT Notification {
@@ -223,6 +224,11 @@ class MESSAGE_CENTER_EXPORT Notification {
   void set_pinned(bool pinned) { optional_fields_.pinned = pinned; }
 #endif  // defined(OS_CHROMEOS)
 
+  // Gets a text for spoken feedback.
+  const base::string16& accessible_name() const {
+    return optional_fields_.accessible_name;
+  }
+
   NotificationDelegate* delegate() const { return delegate_.get(); }
 
   const RichNotificationData& rich_notification_data() const {