don't fail if no classList support

src/ShadowDOM/wrappers/DOMTokenList.js

@@ -14,6 +14,12 @@
 (function(scope) {
   'use strict';
 
+  if (!window.DOMTokenList) {
+    console.warn('Missing DOMTokenList prototype, please include a ' +
+        'compatible classList polyfill such as http://goo.gl/uTcepH.');
+    return;
+  }
+
   var unsafeUnwrap = scope.unsafeUnwrap;
   var enqueueMutation = scope.enqueueMutation;
 

src/ShadowDOM/wrappers/Element.js

@@ -103,6 +103,7 @@
       var list = classListTable.get(this);
       if (!list) {
         list = unsafeUnwrap(this).classList;
+        if (!list) return;
         list.ownerElement_ = this;
         classListTable.set(this, list);
       }

tests/ShadowDOM/js/DOMTokenList.js

@@ -9,6 +9,13 @@
  */
 
 suite('DOMTokenList', function() {
+  if (!window.DOMTokenList) {
+    test('classList returns undefined if not supported', function() {
+      var div = document.createElement('div');
+      assert.isUndefined(div.classList);
+    });
+    return;
+  }
 
   test('instanceof', function() {
     var div = document.createElement('div');