Allow partial update for notification update API

chrome/renderer/resources/extensions/notifications_custom_bindings.js

Index: chrome/renderer/resources/extensions/notifications_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/notifications_custom_bindings.js b/chrome/renderer/resources/extensions/notifications_custom_bindings.js
index 5150a4fb1e4b1a8ee3d7a63f052b9e1394c4e216..6416978a065a0cbee2ca51d12d9a750040f4ce66 100644
--- a/chrome/renderer/resources/extensions/notifications_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/notifications_custom_bindings.js
@@ -22,11 +22,16 @@ function replaceNotificationOptionURLs(notification_details, callback) {
   //  width: (optional) The maximum width of the image to be downloaded.
   //  height: (optional) The maximum height of the image to be downloaded.
   //  callback: A function to be called when the URL is complete. It
-  //    should accept an ImageData object and set the appropriate
-  //    field in the output of create.
+  //    should accept an ImageData object and set the appropriate
+  //    field in the output of create.
+
+  // |iconUrl| might be optional for notification updates.
+  if (!notification_details.iconUrl) {
+    callback(true);

[dewittj, 2013/07/24 23:09:53]

What if all they want to update is the image url, or the button icon urls?  This
logic won't work here.

[jianli, 2013/07/25 01:02:41]

Done.

+    return;
+  }
 
   // TODO(dewittj): Try to remove hard-coding of image sizes.
-  // |iconUrl| is required.
   var url_specs = [{
     path: notification_details.iconUrl,
     width: 80,