[DevTools] Get rid of floats in treeoutline.

third_party/WebKit/Source/devtools/front_end/elements/computedStyleSidebarPane.css

 /*
  * Copyright (c) 2015 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.
  */
 
 .computed-properties {
     -webkit-user-select: text;
 }
 
@@ skipping 71 matching lines @@
 /* FIXME: Patch TreeElement styles to use flex for title layout. */
 
 .tree-outline li {
     display: flex;
     align-items: baseline;
 }
 
 .tree-outline li::before {
     float: none;
     flex: none;
-    -webkit-mask-position: -3px -97px;
     background-color: rgb(110, 110, 110);
     margin-left: 4px;
 }
-
-.tree-outline li.parent.expanded::before {
-    -webkit-mask-position: -19px -97px;
-}