[DevTools] Use ListWidget for rendering of EditFileSystemView.

third_party/WebKit/Source/devtools/front_end/ui/listWidget.css

 /*
  * Copyright 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.
  */
 
 .list {
     flex: auto 0 1;
     overflow-y: auto;
     border: 1px solid rgb(231, 231, 231);
@@ skipping 15 matching lines @@
 
 .list-item:hover {
     background: hsl(0, 0%, 96%);
 }
 
 .controls-container {
     display: flex;
     flex-direction: row;
     justify-content: flex-end;
     align-items: stretch;
+    pointer-events: none;
 }
 
 .controls-gradient {
     flex: 0 1 50px;
 }
 
 .list-item:hover .controls-gradient {
     background-image: linear-gradient(90deg, transparent, hsl(0, 0%, 96%));
 }
 
 .controls-buttons {
     flex: none;
     display: flex;
     flex-direction: row;
     align-items: center;
+    pointer-events: auto;
 }
 
 .list-item:hover .controls-buttons {
     background-color: hsl(0, 0%, 96%);
 }
 
 .remove-button,
 .edit-button {
     background-image: url(Images/toolbarButtonGlyphs.png);
     background-size: 352px 168px;
@@ skipping 61 matching lines @@
 }
 
 .editor-content input {
     margin-right: 10px;
 }
 
 .editor-content input.error-input {
     outline: auto 2px red;
     background-color: white;
 }