DevTools: speed up network scrolling and layout.

Source/devtools/front_end/networkLogView.css

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 273 matching lines @@
     bottom: 0;
     margin: auto -7px;
     height: 13px;
     line-height: 13px;
     font-size: 90%;
     color: rgba(0, 0, 0, 0.75);
     text-shadow: rgba(255, 255, 255, 0.25) 1px 0 0, rgba(255, 255, 255, 0.25) -1px 0 0, rgba(255, 255, 255, 0.333) 0 1px 0, rgba(255, 255, 255, 0.25) 0 -1px 0;
     z-index: 150;
     overflow: hidden;
     text-align: center;
-    opacity: 0;
-    -webkit-transition: opacity 250ms ease-in-out;
+    visibility: hidden;
 }
 
 .network-graph-side:hover .network-graph-label {
-    opacity: 1;
+    visibility: visible;
 }
 
 .network-graph-label:empty {
     display: none;
 }
 
 .network-graph-label.waiting {
     margin-right: 5px;
 }
 
@@ skipping 263 matching lines @@
 }
 
 #network-container:not(.brief-mode) .data-grid tr.selected {
     background-color: transparent;
     color: #222;
 }
 
 #network-container.brief-mode .data-grid .data-container {
     padding-right: 0;
 }