DevTools: migrate SoftContextMenu icons over to UI.Icon

third_party/WebKit/Source/devtools/front_end/ui/softContextMenu.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.
  */
 
 :host {
     position: absolute;
     border: 1px solid rgba(196, 196, 196, 0.9);
     border-top: 1px solid rgba(196, 196, 196, 0.5);
@@ skipping 79 matching lines @@
     flex: 1 1 auto;
     text-align: right;
     padding-left: 10px;
 }
 
 .soft-context-menu-item-mouse-over .soft-context-menu-shortcut {
     color: inherit;
 }
 
 .checkmark {
-    background-image: url(Images/toolbarButtonGlyphs.png);
-    background-size: 352px 168px;
     opacity: 0.7;
-    width: 10px;
-    height: 10px;
-    background-position: -128px -109px;
-    display: inline-block;
     pointer-events: none;
     margin: auto 5px auto 0px;
 }
 
-@media (-webkit-min-device-pixel-ratio: 1.1) {
-.checkmark {
-    background-image: url(Images/toolbarButtonGlyphs_2x.png);
-}
-}
+.soft-context-menu-item-mouse-over .checkmark {
+    opacity: 1;
+}