DevTools: add tooltip for Preserve Log.

Source/devtools/front_end/NetworkPanel.js

 /*
  * Copyright (C) 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2008, 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 632 matching lines @@
         this._recordButton.addEventListener("click", this._onRecordButtonClicked, this);
 
         this._clearButton = new WebInspector.StatusBarButton(WebInspector.UIString("Clear"), "clear-status-bar-item");
         this._clearButton.addEventListener("click", this._reset, this);
 
         this._largerRequestsButton = new WebInspector.StatusBarButton(WebInspector.UIString("Use small resource rows."), "network-larger-resources-status-bar-item");
         this._largerRequestsButton.toggled = WebInspector.settings.resourcesLargeRows.get();
         this._largerRequestsButton.addEventListener("click", this._toggleLargerRequests, this);
 
         this._preserveLogCheckbox = new WebInspector.StatusBarCheckbox(WebInspector.UIString("Preserve log"));
+        this._preserveLogCheckbox.element.title = WebInspector.UIString("Do not clear log on page reload / navigation.");
     },
 
     _loadEventFired: function(event)
     {
         if (!this._recordButton.toggled)
             return;
 
         this._mainRequestLoadTime = event.data || -1;
         // Schedule refresh to update boundaries and draw the new line.
         this._scheduleRefresh();
@@ skipping 2228 matching lines @@
 WebInspector.NetworkDataGridNode.RequestPropertyComparator = function(propertyName, revert, a, b)
 {
     var aValue = a._request[propertyName];
     var bValue = b._request[propertyName];
     if (aValue > bValue)
         return revert ? -1 : 1;
     if (bValue > aValue)
         return revert ? 1 : -1;
     return 0;
 }