Reattach Restart Chrome Event Handler to Experiment Restart Button

BUG=925720

Change-Id: Ia7561fd1153408df32509cb96a313cc439193567
Reviewed-on: https://chromium-review.googlesource.com/c/1439924
Commit-Queue: Robert Liao <robliao@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Auto-Submit: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626776}

components/flags_ui/resources/flags.js

@@ -44,9 +44,10 @@ function renderTemplate(experimentalFeaturesData) {
     };
   }
 
-  elements = document.getElementsByClassName('experiment-restart-button');
-  for (var i = 0; i < elements.length; ++i) {
-    elements[i].onclick = restartBrowser;
+  var element = $('experiment-restart-button');
+  assert(element || cr.isIOS);
+  if (element) {
+    element.onclick = restartBrowser;
   }
 
   // Tab panel selection.