DevTools: render category filters in a way that they don't clash.

Source/devtools/front_end/timeline/timelinePanel.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 567 matching lines @@
     background-image: url(Images/checker.png);
     -webkit-user-select: text;
     -webkit-user-drag: auto;
 }
 
 .image-container {
     padding: 0;
 }
 
 .timeline-filters-header {
-    flex: 0 0 23px;
     overflow: hidden;
+    flex: none;
 }
 
 .timeline-details {
     vertical-align: top;
 }
 
 .timeline-details-title {
     border-bottom: 1px solid #B8B8B8;
     font-weight: bold;
     padding-bottom: 5px;
@@ skipping 262 matching lines @@
 .timeline-gap {
     flex: none;
 }
 
 .timeline-filmstrip-preview {
     margin-top: 10px;
     max-width: 200px;
     max-height: 200px;
     cursor: pointer;
 }