Incognito NTP style tweaks

ui/webui/resources/css/text_defaults_md.css

-/* Copyright 2014 The Chromium Authors. All rights reserved.
+/* 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. */
 
 /* This file is dynamically processed by a C++ data source handler to fill in
  * some per-platform/locale styles that dramatically alter the page. This is
  * done to reduce flicker, as JS may not run before the page is rendered.
  *
  * There are two ways to include this stylesheet:
  * 1. via its chrome://resources/ URL in HTML, i.e.:
  *
- *   <link rel="stylesheet" href="chrome://resources/css/text_defaults.css">
+ *   <link rel="stylesheet" href="chrome://resources/css/text_defaults_md.css">
  *
- * 2. via the webui::AppendWebUICSSTextDefaults() method to directly append it
+ * 2. via the webui::AppendWebUICSSTextDefaultsMd() method to directly append it
  * to an HTML string.
  * Otherwise its $placeholders won't be expanded. */
 
+@import url(chrome://resources/css/roboto.css);
+
 html {
   direction: ${textDirection};
 }
 
 body {
-  font-family: ${fontFamily};
+  font-family: Roboto, ${fontFamily};
   font-size: ${fontSize};
 }
 
 button {
-  font-family: ${fontFamily};
+  font-family: Roboto, ${fontFamily};
 }