DevTools: fix selected tab rendering on non-default zoom levels.

Source/devtools/front_end/ui/tabbedPane.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * 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
@@ skipping 204 matching lines @@
     cursor: pointer !important;
 }
 
 .tabbed-pane-shadow.vertical-tab-layout .tabbed-pane-header-tab.selected {
     color: inherit;
     border: none transparent;
     border-left: 6px solid #666;
 }
 
 .tabbed-pane-tab-slider {
-    width: 1px;
     height: 2px;
     position: absolute;
     bottom: 0;
     background-color: #3E82F7;
     left: 0;
     z-index: 50;
     transform-origin: 0 0;
     transition: transform 150ms cubic-bezier(0, 0, 0.2, 1);
     visibility: hidden;
 }
 
 .tabbed-pane-tab-slider.enabled {
     visibility: visible;
 }
 
 .tabbed-pane-header.tabbed-pane-no-header-background {
     background-color: transparent;
 }