DevTools Timeline: remove hard-coded pixel-sized adjustments from overview's CSS

Source/devtools/front_end/TimelineOverviewPane.js

 /*
  * 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 30 matching lines @@
     this._windowStartTime = 0;
     this._windowEndTime = Infinity;
     this._eventDividers = [];
 
     this._model = model;
 
     this._topPaneSidebarElement = document.createElement("div");
     this._topPaneSidebarElement.id = "timeline-overview-sidebar";
 
     var overviewTreeElement = document.createElement("ol");
-    overviewTreeElement.className = "sidebar-tree";
+    overviewTreeElement.className = "sidebar-tree vbox";
     this._topPaneSidebarElement.appendChild(overviewTreeElement);
     this.element.appendChild(this._topPaneSidebarElement);
 
     var topPaneSidebarTree = new TreeOutline(overviewTreeElement);
 
     this._overviewItems = {};
     this._overviewItems[WebInspector.TimelineOverviewPane.Mode.Events] = new WebInspector.SidebarTreeElement("timeline-overview-sidebar-events",
         WebInspector.UIString("Events"));
     this._overviewItems[WebInspector.TimelineOverviewPane.Mode.Frames] = new WebInspector.SidebarTreeElement("timeline-overview-sidebar-frames",
         WebInspector.UIString("Frames"));
@@ skipping 889 matching lines @@
 WebInspector.TimelineWindowFilter.prototype = {
     /**
      * @param {!WebInspector.TimelinePresentationModel.Record} record
      * @return {boolean}
      */
     accept: function(record)
     {
         return record.lastChildEndTime >= this._pane._windowStartTime && record.startTime <= this._pane._windowEndTime;
     }
 }