Adds the contextMessage field to notifications.

chrome/common/extensions/api/notifications.idl

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Use the <code>chrome.notifications</code> API to create rich notifications
 // using templates and show these notifications to users in the system tray.
 namespace notifications {
   [noinline_doc] enum TemplateType {
     // icon, title, message, expandedMessage, up to two buttons
     basic,
@@ skipping 35 matching lines @@
     // Sender's avatar, app icon, or a thumbnail for image notifications.
     DOMString? iconUrl;
     [nodoc] NotificationBitmap? iconBitmap;
 
     // Title of the notification (e.g. sender name for email).
     DOMString? title;
 
     // Main notification content.
     DOMString? message;
 
+    // Alternate notification content with a lower-weight font.
+    [nodoc] DOMString? contextMessage;
+
     // Priority ranges from -2 to 2. -2 is lowest priority. 2 is highest. Zero
     // is default.
     long? priority;
 
     // A timestamp associated with the notification, in milliseconds past the
     // epoch (e.g. <code>Date.now() + n</code>).
     double? eventTime;
 
     // Text and icons for up to two notification action buttons.
     NotificationButton[]? buttons;
@@ skipping 53 matching lines @@
     static void onClosed(DOMString notificationId, boolean byUser);
 
     // The user clicked in a non-button area of the notification.
     static void onClicked(DOMString notificationId);
 
     // The user pressed a button in the notification.
     static void onButtonClicked(DOMString notificationId, long buttonIndex);
   };
 
 };