Fix reference error in JS code

Bug: 881316
Change-Id: I0139ded58d3d76c1bded1cc21f67efefd26322f5
Reviewed-on: https://chromium-review.googlesource.com/1210745
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Ravi Mistry <rmistry@chromium.org>
diff --git a/src/main/resources/static/chumpdetector.js b/src/main/resources/static/chumpdetector.js
index eb87782..2d4c692 100644
--- a/src/main/resources/static/chumpdetector.js
+++ b/src/main/resources/static/chumpdetector.js
@@ -485,7 +485,7 @@
 
 // Add a message div to appear inside the confirm submit dialog.
 var confirmSubmitMessage = document.createElement('p');
-plugin.hook('confirm-submit-change').onAttached(function(element) {
+self.hook('confirm-submit-change').onAttached(function(element) {
   element.appendChild(confirmSubmitMessage);
 });