title: How to programmatically add tooltip to a combobox
body: <p>I'm trying to add a tip to a <code>combobox</code> during runtime with the code below but it doesn't work:</p>
  
  <pre><code>onStartReport: function (aButton) {
      var lTip = Ext.getCmp('datasources');
      lTip.setTooltip("Information on datasource");
  }
  </code></pre>
  
  <p>I also tried with this, but I get an error:</p>
  
  <pre><code>onStartReport: function (aButton) {
       var tip = Ext.create('Ext.tip.ToolTip', {
       target: 'datasources',
       html: 'Information on datasource'
       });        
  }
  </code></pre>
  
  <p>view classic:</p>
  
  <pre><code>{
      xtype: 'combo',
      itemId: 'datasources',
      name: 'datasources',
      fieldLabel: 'Data sources',
      displayField: 'description',
      valueField: 'id',
      queryMode: 'local',
      value: 0,
      forceSelection: true,
      editable: false,   
      store: {
          data: [
              {id: 0, description: 'OnLine'},
              {id: 1, description: 'History'}
          ],
          fields: [
              {name: 'id', type: 'int'},
              {name: 'description', type: 'string'}               
          ],
          autoLoad: true
      }
  }
  </code></pre>