Add Roboto-Medium webfont and factor out common Roboto WebUI CSS file.

chrome/browser/resources/pdf/index-material.css

Index: chrome/browser/resources/pdf/index-material.css
diff --git a/chrome/browser/resources/pdf/index-material.css b/chrome/browser/resources/pdf/index-material.css
index 5d7784eec29b6a3c67e37823170c0a2568d0d4aa..743fdb5a8900bd879471e667ddfbab186415f35f 100644
--- a/chrome/browser/resources/pdf/index-material.css
+++ b/chrome/browser/resources/pdf/index-material.css
@@ -2,14 +2,6 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
-@font-face {
-  font-family: 'Roboto';
-  font-style: normal;
-  font-weight: 400;
-  src: local('Roboto Regular'), local('Roboto-Regular'), url(chrome://resources/roboto/roboto.woff2) format('woff2');
-  unicode-range: U+0460-052F, U+20B4, U+2DE0-2DFF, U+A640-A69F;
-}
-
 body {
   background-color: #424242;
   font-family: Roboto, 'Helvetica Neue', Helvetica, Arial;