Switch tracing to new flexbox.

tracing/tracing/ui/extras/chrome/cc/layer_picker.css

 /* Copyright (c) 2013 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.
  */
 
 * /deep/ tr-ui-e-chrome-cc-layer-picker {
-  -webkit-flex-direction: column;
-  display: -webkit-flex;
+  flex-direction: column;
+  display: flex;
 }
 
 * /deep/ tr-ui-e-chrome-cc-layer-picker > top-controls {
-  -webkit-flex: 0 0 auto;
+  flex: 0 0 auto;
   background-image: -webkit-gradient(linear,
                                      0 0, 100% 0,
                                      from(#E5E5E5),
                                      to(#D1D1D1));
   border-bottom: 1px solid #8e8e8e;
   border-top: 1px solid white;
   display: inline;
   font-size: 14px;
   padding-left: 2px;
 }
 
 * /deep/ tr-ui-e-chrome-cc-layer-picker > top-controls input[type='checkbox'] {
     vertical-align: -2px;
 }
 
 * /deep/ tr-ui-e-chrome-cc-layer-picker > .x-list-view {
-  -webkit-flex: 1 1 auto;
+  flex: 1 1 auto;
   font-family: monospace;
   overflow: auto;
 }
 
 * /deep/ tr-ui-e-chrome-cc-layer-picker > tr-ui-a-generic-object-view {
-  -webkit-flex: 0 0 auto;
+  flex: 0 0 auto;
   height: 200px;
   overflow: auto;
 }
 
 * /deep/ tr-ui-e-chrome-cc-layer-picker > tr-ui-a-generic-object-view * {
   -webkit-user-select: text !important;
   cursor: text;
 }