DevTools: empty user agent validation

third_party/WebKit/Source/devtools/front_end/network/networkConfigView.css

 /*
  * Copyright (c) 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.
  */
 
 .network-config {
     padding: 12px;
     display: block;
 }
@@ skipping 65 matching lines @@
 }
 
 .network-config-ua input[readonly] {
     background-color: rgb(235, 235, 228);
 }
 
 .network-config-ua input[type=text], .network-config-ua .chrome-select {
     margin-top: 8px;
 }
 
+.network-config-ua input[type="text"]:invalid {
+    outline: auto red;
+}
+
 .network-config-ua .chrome-select {
     width: calc(100% - 20px);
     max-width: 250px;
 }
 
 .network-config-ua label[is="dt-radio"] {
     display: block;
 }
 
 .network-config-ua-auto, .network-config-ua-custom {
     opacity: 0.5;
 }
 
 .network-config-ua-auto.checked, .network-config-ua-custom.checked {
     opacity: 1;
 }