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diff --git a/catapult/third_party/polymer/components/shadycss/src/document-wait.js b/catapult/third_party/polymer/components/shadycss/src/document-wait.js
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+/**
+@license
+Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+*/
+
+'use strict';
+
+/** @type {Promise<void>} */
+let readyPromise = null;
+
+/** @type {?function(?function())} */
+let whenReady = window['HTMLImports'] && window['HTMLImports']['whenReady'] || null;
+
+/** @type {function()} */
+let resolveFn;
+
+/**
+ * @param {?function()} callback
+ */
+export default function documentWait(callback) {
+  requestAnimationFrame(function() {
+    if (whenReady) {
+      whenReady(callback)
+    } else {
+      if (!readyPromise) {
+        readyPromise = new Promise((resolve) => {resolveFn = resolve});
+        if (document.readyState === 'complete') {
+          resolveFn();
+        } else {
+          document.addEventListener('readystatechange', () => {
+            if (document.readyState === 'complete') {
+              resolveFn();
+            }
+          });
+        }
+      }
+      readyPromise.then(function(){ callback && callback(); });
+    }
+  });
+}