Change security panel overview to support neutral icons.

Source/devtools/front_end/security/lockIcon.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.
  */
 
 .lock-icon {
     background-size: cover;
     height: 16px;
     width: 16px;
 }
 
 .lock-icon-unknown {
-    background-image: url(Images/securityStateHttp.png);
+    background-image: url(Images/securityStateNeutral.png);
 }
 
-.lock-icon-http {
-    background-image: url(Images/securityStateHttp.png);
+.lock-icon-neutral {
+    background-image: url(Images/securityStateNeutral.png);
 }
 
 .lock-icon-insecure {
     background-image: url(Images/securityStateInsecure.png);
 }
 
 .lock-icon-warning {
     background-image: url(Images/securityStateWarning.png);
 }
 
 .lock-icon-secure {
     background-image: url(Images/securityStateSecure.png);
 }
 
 
 @media (-webkit-min-device-pixel-ratio: 1.5) {
     .lock-icon-unknown {
-        background-image: url(Images/securityStateHttp_2x.png);
+        background-image: url(Images/securityStateNeutral_2x.png);
     }
 
-    .lock-icon-http {
-        background-image: url(Images/securityStateHttp_2x.png);
+    .lock-icon-neutral {
+        background-image: url(Images/securityStateNeutral_2x.png);
     }
 
     .lock-icon-insecure {
         background-image: url(Images/securityStateInsecure_2x.png);
     }
 
     .lock-icon-warning {
         background-image: url(Images/securityStateWarning_2x.png);
     }
 
     .lock-icon-secure {
         background-image: url(Images/securityStateSecure_2x.png);
     }
 }
 
 .sidebar-tree-item .lock-icon {
     float: left;
     margin-right: 2px;
 }