Add TRACE_COUNTER support to about:tracing

chrome/browser/resources/tracing/timeline.css

 /*
 Copyright (c) 2011 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.
 */
 
 .timeline-drag-box {
   background-color: rgba(0, 0, 255, 0.25);
   border: 1px solid #000060
   font-size: 75%;
   position: fixed;
 }
 
 .timeline-thread-track {
   -webkit-box-orient: vertical;
   display: -webkit-box;
   padding: 1px 0;
 }
 
 .timeline-thread-track:not(:first-child) {
   border-top: 1px solid #D0D0D0;
 }
 
-.timeline-slice-track {
+.timeline-canvas-based-track {
   -webkit-box-orient: horizontal;
   -webkit-box-align: stretch;
   background-color: white;
   display: -webkit-box;
-  height: 18px;
   margin: 0;
   padding: 0;
   padding-right: 5px;
 }
 
-.timeline-slice-track-title {
+.timeline-canvas-based-track-title {
   overflow: hidden;
   padding-right: 5px;
   text-align: right;
   text-overflow: ellipsis;
   white-space: nowrap;
 }
 
-.timeline-slice-track-canvas-container {
+.timeline-canvas-based-track-canvas-container {
   -webkit-box-flex: 1;
   width: 100%;
 }
 
-.timeline-slice-track-canvas {
+.timeline-canvas-based-track-canvas {
   -webkit-box-flex: 1;
   height: 100%;
   width: 100%;
 }
+
+.timeline-slice-track {
+  height: 18px;
+}
+
+.timeline-counter-track {
+  height: 30px;
+}