add font rules to log widget

pkg/polymer/lib/src/build/log_injector.css

 /** Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
     for details. All rights reserved. Use of this source code is governed by a
     BSD-style license that can be found in the LICENSE file. **/
 .build-logs {
   position: fixed;
   bottom: 0;
   right: 0;
   max-width: 50%;
   z-index: 10000;
+  font-family: sans-serif !important;
 }
 .build-logs .log {
   padding: 0.6em;
   background: black;
   color: white;
   border: solid 1px #666;
   border-bottom: 0px;
 }
 .build-logs .fine {
   color: green;
@@ skipping 46 matching lines @@
   display: none;
 }
 .build-logs .content > div.active {
   display: block;
 }
 
 .build-logs .content span.text {
   padding: 0.4em 0.2em 0.2em 2em;
   white-space: pre;
   display: block;
-  font-family: monospace;
+  font-family: monospace !important;
 }