Remove all usage of -webkit-*gradient inside blink

Source/devtools/front_end/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 67 matching lines @@
     border: 0 none;
     -webkit-flex: none;
 }
 
 .audit-launcher-view button {
     margin: 0 5px 0 0;
 }
 
 .audit-launcher-view button:active {
     background-color: rgb(215, 215, 215);
-    background-image: -webkit-gradient(linear, left top, left bottom, from(rgb(194, 194, 194)), to(rgb(239, 239, 239)));
+    background-image: linear-gradient(to bottom, rgb(194, 194, 194), rgb(239, 239, 239));
 }
 
 .panel-enabler-view.audit-launcher-view label {
     padding: 0 0 5px 0;
     margin: 0;
     -webkit-flex: none;
 }
 
 .panel-enabler-view.audit-launcher-view label.disabled {
     color: rgb(130, 130, 130);
@@ skipping 136 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;
 }