I want to put file upload button in a toolbar and make it look like other toolbar buttons.

I made a formpanel and put it to a toolbar like regular item:
Code:
var file_form = Ext.create('Ext.form.FormPanel',{
        baseCls: ''
        ,width: 110
        ,items: [
           Ext.create('Ext.form.File', {
                buttonOnly: true,
                hideLabel: true,
                buttonText: 'Upload'
                ,buttonCfg: {
                    icon: '/images/icons/add.png'
                }
                ,name: 'img'
                ,listeners: {
                    change: function(t,v){
                        // submit form
                    }
                }
            })
       ]
    })
What I get is a regular grey button in a toolbar. Uploading works fine.
But in B3 buttonCfg does not make any changes - icon not appears (in B2 it worked).
I tried to play with different classes in button config but all in vain.

Any ideas how to make it look like toolbar button?

Thanks.