title: How to update tool tip content when grid store is update?
body: <p>I have this.mygrid there is column as <code>my_col_id</code> i want to add tool tip in to the grid cell. I added tool tip for grid cell but that tool tip not update with my store(<code>my_store</code>) changes. how to update my grid tool tip when store update</p>
  
  <p>Note: don't work when i added colName.render in to the store update method </p>
  
  <pre><code>initComponent{
      colName = this.mygrid.getColumnModel().getColumnById('my_col_id');
      colName.renderer  = this.addToolTip;
  }    
     addToolTip : function(value, metadata, record, rowIndex, colIndex, store){
        metadata.attr = 'ext:qtip="' + record.get('PRICE')+'&lt;br&gt;'+record.get('DATE') + '"';
        return value;
     } 
  </code></pre>