DevTools: migrate elements panel gutter icon to UI.Icon

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

 /*
  * Copyright (c) 2014 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.
  */
 
 .elements-disclosure {
     width: 100%;
     display: inline-block;
     line-height: normal;
@@ skipping 303 matching lines @@
     color: white;
 }
 
 ol:focus li.selected .webkit-html-attribute-name {
     color: #ccc;
 }
 
 .elements-disclosure .gutter-container {
     position: absolute;
     top: 0;
-}
-
-.elements-disclosure li.selected .gutter-container:not(.has-decorations) {
-    left: 0px;
-    width: 16.25px;
-    height: 18px;
-    transform: rotate(-90deg) translateX(-13px) scale(0.8);
-    transform-origin: 0% 0%;
-    -webkit-mask-image: url(Images/toolbarButtonGlyphs.png);
-    -webkit-mask-position: -201px -27px;
-    -webkit-mask-size: 352px 168px;
-    background-color: white;
+    left: 0;
     cursor: pointer;
 }
 
-@media (-webkit-min-device-pixel-ratio: 1.1) {
-.elements-disclosure li.selected .gutter-container:not(.has-decorations) {
-    -webkit-mask-image: url(Images/toolbarButtonGlyphs_2x.png);
+.gutter-menu-icon {
+    display: none;
+    transform: rotate(-90deg) scale(0.8);
+    background-color: white;
+    position: relative;
+    left: -7px;
+    top: -3px;
 }
-} /* media */
+
+.elements-disclosure li.selected .gutter-container:not(.has-decorations) .gutter-menu-icon {
+    display: block;
+}
 
 /** Guide line */
 li.selected {
     z-index: 0;
 }
 
 li.hovered:not(.always-parent) + ol.children, .elements-tree-outline ol.shadow-root, li.selected:not(.always-parent) + ol.children {
     margin-left: 5px;
     -webkit-padding-start: 6px;
     border-width: 1px;
     border-left-style: solid;
 }
 
 li.hovered:not(.always-parent) + ol.children:not(.shadow-root) {
     border-color: hsla(0,0%,0%,0.1);
 }
 
 .elements-tree-outline ol.shadow-root {
     border-color: hsla(0,0%,80%,1);
 }
 
 li.selected:not(.always-parent) + ol.children {
     border-color: hsla(216,68%,80%,1) !important;
 }