DevTools: only set title w/ shortcut via Tooltip manager API.

Source/devtools/front_end/ui/treeoutline.js

 /*
  * Copyright (C) 2007 Apple 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
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 580 matching lines @@
                 this._listItemNode.appendChild(this._title);
             this._ensureSelection();
         }
     },
 
     /**
      * @param {string} x
      */
     set tooltip(x)
     {
-        WebInspector.Tooltip.install(this._listItemNode, x);
+        this._listItemNode.title = x;
     },
 
     /**
      * @return {boolean}
      */
     isExpandable: function()
     {
         return this._expandable;
     },
 
@@ skipping 456 matching lines @@
     isEventWithinDisclosureTriangle: function(event)
     {
         // FIXME: We should not use getComputedStyle(). For that we need to get rid of using ::before for disclosure triangle. (http://webk.it/74446)
         var paddingLeftValue = window.getComputedStyle(this._listItemNode).paddingLeft;
         console.assert(paddingLeftValue.endsWith("px"));
         var computedLeftPadding = parseFloat(paddingLeftValue);
         var left = this._listItemNode.totalOffsetLeft() + computedLeftPadding;
         return event.pageX >= left && event.pageX <= left + TreeElement._ArrowToggleWidth && this._expandable;
     }
 }