DevTools: polish Mac UI (borders, alignment, line heights, images).

Source/devtools/front_end/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 57 matching lines @@
 }
 
 .tabbed-pane-header-tab {
     float: left;
     margin-top: 2px;
     padding: 2px 4px 2px 4px;
     height: 21px;
     border: 1px solid transparent;
     border-bottom: none;
     line-height: 15px;
-    
     white-space: nowrap;
     text-overflow: ellipsis;
     overflow: hidden;
     cursor: default;
 }
 
 .tabbed-pane-header-tab.measuring {
     visibility: hidden;
 }
 
@@ skipping 61 matching lines @@
 .tabbed-pane-header-tabs-drop-down > select.drop-down-menu {
     position: absolute;
     top: 0;
     right: 0;
     bottom: 0;
     left: 0;
     opacity: 0;
     font-size: 75%;
     width: 20px;
 }