Convert Media Router WebUI <button>s to <paper-button>s.

chrome/browser/resources/media_router/media_router_common.css

Index: chrome/browser/resources/media_router/media_router_common.css
diff --git a/chrome/browser/resources/media_router/media_router_common.css b/chrome/browser/resources/media_router/media_router_common.css
index 00597408cd50f893084e96a6e9e117c01a809053..47d72ae207cfef5481805cd766f00c53bb4725cb 100644
--- a/chrome/browser/resources/media_router/media_router_common.css
+++ b/chrome/browser/resources/media_router/media_router_common.css
@@ -2,13 +2,13 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
-button {
-  border: 1px solid rgb(193, 193, 195);
+.button {
+  /* TODO(apacible): Update to use Chromium paper color. */
+  background-color: rgb(238, 238, 238);
   color: rgb(44, 44, 44);
   cursor: pointer;
   font-size: 1em;
   font-weight: bold;
-  height: 32px;
   overflow: hidden;
   text-align: center;
   width: 100%;