[NTP] Fix cancel button submitting when adding custom link

"Cancel" was calling the form's submit event, which triggered the add
link flow.

Bug: 874018
Change-Id: Iad822d3884484f5dc0d9f3e6667c9d4c9e0a2728
Reviewed-on: https://chromium-review.googlesource.com/1174908Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Kristi Park <kristipark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583004}

chrome/browser/resources/local_ntp/custom_links_edit.js

@@ -337,10 +337,10 @@ function init() {
   });
   $(IDS.DELETE).addEventListener('click', deleteLink);
   $(IDS.CANCEL).addEventListener('click', closeDialog);
+  $(IDS.DONE).addEventListener('click', finishEditLink);
   $(IDS.FORM).addEventListener('submit', (event) => {
     // Prevent the form from submitting and modifying the URL.
     event.preventDefault();
-    finishEditLink();
   });
   let finishEditOrClose = (event) => {
     if (event.keyCode === KEYCODES.ENTER) {