title: Create dymanic tab and load the data from the url is not working
body: <p>I have created the dynamic tab but not able to load the data from the url.</p>
  
  <pre><code>Ext.onReady(function() {
  
  
      var tabs = new Ext.TabPanel({
          region:'center',
          activeTab:0,
          margins: '5 5 5 0',
  
          resizeTabs:true, 
          minTabWidth: 115,
          items:[{ 
              title: 'Dashboard',
              contentEl: 'simple-form',
              closable:true
          }]
  
      });
  
      var viewport = new Ext.Viewport({
          layout:'border', 
          defaults: {
              collapsible: false,
              split: true
          },
          items: [{    
              title:'PSL Admin',
              region: 'north',
              contentEl: 'north', 
              margins: '5 5 5 5',
              split:false 
          },{
              title:'Navigation',
              collapsible: true, 
              region:'west',
              contentEl: 'west', 
              margins: '5 0 5 5',
              cmargins: '5 5 5 5',
              width: 175,
              minSize: 100,
              maxSize: 250 
          },
  
          tabs 
          ]
  
      });
  
      function addTab(){
         tabs.add({
          title: 'Bar',
          closable: true,
          plain: true,
          loader: {
              autoLoad:true,
              url :'test.html'
          }
  
          });
  
      }
  
      Ext.get('add').on('click', function(){
          addTab();
      });
  
  });
  </code></pre>
  
  <p>Whenever I am clicking the button just calling the above function, I can see the tab, but content is not loaded.</p>
  
  <p>Can anyone help where am I wrong?</p>