sync-confirmation WebUI: Fix action button handling.

Take into account that in Shadow DOM v1 document-fragment elements are reported
in an Event's path.

Bug: 897168
Change-Id: I95d16b46ec2b66244b03f5b9aec98d0ca6dc7abc
Reviewed-on: https://chromium-review.googlesource.com/c/1294422Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601762}

chrome/browser/resources/signin/dice_sync_confirmation/sync_confirmation_app.js

@@ -93,8 +93,10 @@ Polymer({
    */
   getConsentConfirmation_: function(path) {
     for (var element of path) {
-      if (element.hasAttribute('consent-confirmation'))
+      if (element.nodeType !== Node.DOCUMENT_FRAGMENT_NODE &&
+          element.hasAttribute('consent-confirmation')) {
         return element.innerHTML.trim();
+      }
     }
     assertNotReached('No consent confirmation element found.');
     return '';

chrome/browser/resources/signin/sync_confirmation/sync_confirmation.js

@@ -14,8 +14,10 @@ cr.define('sync.confirmation', function() {
   function getConsentConfirmation(path) {
     var consentConfirmation;
     for (var element of path) {
-      if (element.hasAttribute('consent-confirmation'))
+      if (element.nodeType !== Node.DOCUMENT_FRAGMENT_NODE &&
+          element.hasAttribute('consent-confirmation')) {
         return element.innerHTML.trim();
+      }
     }
     assertNotReached('No consent confirmation element found.');
     return '';