DevTools: Make labeled checkbox a web component

Source/devtools/front_end/components/breakpointsList.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 54 matching lines @@
     text-overflow: ellipsis;
     overflow: hidden;
     padding: 2px 0;
 }
 
 .breakpoint-list li:hover {
     background-color: rgba(56, 121, 217, 0.2);
 }
 
 .breakpoint-list .checkbox-elem {
-    font-size: 10px;
     margin: 0 4px;
     vertical-align: top;
     position: relative;
     z-index: 1;
-    top: 3px;
 }
 
 .breakpoint-list .source-text {
     white-space: nowrap;
     text-overflow: ellipsis;
     overflow: hidden;
-    margin: 2px 0 0 20px;
 }
 
 .sidebar-pane .breakpoint-hit {
     background-color: rgb(255, 255, 194);
 }
 
 li.breakpoint-hit .breakpoint-hit-marker {
     background-color: rgb(255, 255, 194);
     height: 18px;
     left: 0;
     margin-top: -16px;
     position: absolute;
     right: 0;
     z-index: -1;
 }
 
 .event-listener-breakpoints.properties-tree li {
     height: 16px;
     padding-top: 3px;
 }
 
 .event-listener-breakpoints.properties-tree .children li {
     margin-left: 12px;
     height: 16px;
 }
 
 .event-listener-breakpoints .checkbox-elem {
-    float: left;
-    position: relative;
-    top: 1px;
     font-size: 10px;
 }