Adds the contextMessage field to notifications.

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 6a742e03748d3c860e189e6c1ffd39d8f376e931..df7cb5a4bd0cc92eae6ac9622f93348aa229ce6b 100644
--- a/ui/message_center/notification.h
+++ b/ui/message_center/notification.h
@@ -43,6 +43,7 @@ class MESSAGE_CENTER_EXPORT RichNotificationData {
   bool never_timeout;
   base::Time timestamp;
   string16 expanded_message;
+  string16 context_message;
   gfx::Image image;
   std::vector<NotificationItem> items;
   int progress;
@@ -101,6 +102,13 @@ class MESSAGE_CENTER_EXPORT Notification {
     optional_fields_.expanded_message = expanded_message;
   }
 
+  const string16& context_message() const {
+    return optional_fields_.context_message;
+  }
+  void set_context_message(const string16& context_message) {
+    optional_fields_.context_message = context_message;
+  }
+
   const std::vector<NotificationItem>& items() const {
     return optional_fields_.items;
   }