MD Downloads: preload bold Roboto in a better way

chrome/browser/resources/md_downloads/downloads.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-window.addEventListener('load', downloads.Manager.onLoad);
+window.addEventListener('load', function() {
+  downloads.Manager.onLoad();
+
+  if (!cr.isChromeOS) {
+    // TODO(dbeam): this is copied out of roboto.css. I excluded roboto.css from
+    // vulcanize.py and tried to re-use the "src:" rule from the file via
+    // querySelector(href$=roboto.css).sheet.rules[2].style.src, but alas .rules
+    // can't be accessed because the origins don't match (chrome://resources vs
+    // chrome://downloads). So it's duplicated.
+    new FontFace('Roboto', "local('Roboto Bold'), local('Roboto-Bold'), " +
+        "url(chrome://resources/roboto/roboto-bold.woff2) format('woff2')",
+        {weight: 'bold'}).load();
+  }
+});