DevTools: CssChecker: avoid selector crafting in AuditsPanel.

Source/devtools/front_end/audits/auditsPanel.css

 /*
  * Copyright (C) 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 103 matching lines @@
     left: 0;
     right: 0;
     bottom: 0;
     display: none;
 }
 
 .audit-result-view.visible {
     display: block;
 }
 
-.audit-result-view .severity-severe,
-.audit-result-view .severity-warning,
-.audit-result-view .severity-info {
+.audit-result-view .severity {
     background-image: url(Images/statusbarButtonGlyphs.png);
     background-size: 320px 144px;
     display: inline-block;
     width: 10px;
     margin-right: -10px;
     height: 10px;
     position: relative;
     left: -28px;
     margin-top: 3px;
 }
 
 @media (-webkit-min-device-pixel-ratio: 1.5) {
-.audit-result-view .severity-severe,
-.audit-result-view .severity-warning,
-.audit-result-view .severity-info {
+.audit-result-view .severity {
     background-image: url(Images/statusbarButtonGlyphs_2x.png);
 }
 } /* media */
 
-.audit-result-view .severity-severe {
+.audit-result-view .severity.severe {
     background-position: -224px -96px;
 }
 
-.audit-result-view .severity-warning {
+.audit-result-view .severity.warning {
     background-position: -246px -96px;
 }
 
-.audit-result-view .severity-info {
+.audit-result-view .severity.info {
     background-position: -235px -96px;
 }
 
 .audit-result-tree li.parent::before {
     -webkit-user-select: none;
     background-image: url(Images/statusbarButtonGlyphs.png);
     background-size: 320px 144px;
     opacity: 0.5;
     float: left;
     width: 8px;
@@ skipping 76 matching lines @@
     font-weight: bold;
 }
 
 .audit-launcher-view .progress-bar-container {
     display: inline-block;
 }
 
 .audit-launcher-view .progress-bar-container .progress-bar-stop-button {
     display: none;
 }