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

chrome/browser/resources/contextual_search/promo.css

Index: chrome/browser/resources/contextual_search/promo.css
diff --git a/chrome/browser/resources/contextual_search/promo.css b/chrome/browser/resources/contextual_search/promo.css
index 63fe3392ee401b7ad2ca51b0702e639840192146..fdbaa392cb3ceb32acaef99f9bed4aa1f8e3d034 100644
--- a/chrome/browser/resources/contextual_search/promo.css
+++ b/chrome/browser/resources/contextual_search/promo.css
@@ -2,15 +2,6 @@
    Use of this source code is governed by a BSD-style license that can be
    found in the LICENSE file. */
 
-/* TODO: Need to clean up @font-face after we remove font-family from body. */
-@font-face {
-  font-family: 'Roboto2';
-  font-weight: 400;
-  src: local('Roboto'), local('Roboto2-Regular'),
-      url(chrome://resources/roboto/roboto.woff2) format('woff2'),
-      url(chrome://resources/roboto/roboto.woff) format('woff');
-}
-
 /* TODO(pedrosimonetti): Find a better way to fix the problem when the
  * text scaling preference is set to a high value.
  *
@@ -26,7 +17,7 @@
 }
 
 body {
-  font-family: 'Roboto2', sans-serif;
+  font-family: 'Roboto', sans-serif;
   margin: 0;
 }
 
@@ -132,7 +123,7 @@ button {
   background: none;
   border: none;
   display: inline-block;
-  font-family: 'Roboto2', sans-serif;
+  font-family: 'Roboto', sans-serif;
   font-size: 14px;
   margin: 6px 0;
   /* We use a slightly different top-bottom padding because Roboto has a