DevTools: Show asynchronous call stacks on frontend.

Source/devtools/front_end/inspector.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 1387 matching lines @@
 .outline-disclosure ol.children {
     display: none;
 }
 
 .outline-disclosure ol.children.expanded {
     display: block;
 }
 
 .placard {
     position: relative;
+    border-top: 1px solid transparent;
     padding: 3px 8px 4px 18px;
     min-height: 18px;
     white-space: nowrap;
 }
 
+.placard.grouped {
+    padding-left: 36px;
+}
+
 .placard:nth-of-type(2n) {
     background-color: rgb(234, 243, 255);
 }
 
 .placard.selected {
     border-top: 1px solid rgb(172, 172, 172);
     background-image: -webkit-gradient(linear, left top, left bottom, from(rgb(182, 182, 182)), to(rgb(162, 162, 162)));
     background-origin: padding-box;
     background-clip: padding-box;
 }
@@ skipping 1393 matching lines @@
     display: inline-block;
     float: right;
     padding-right: 4px;
     padding-top: 4px;
     padding-left: 2px;
 }
 
 body.undocked .toolbar-close-button-item {
     display: none;
 }