In modern toollkit in Ext.Component the resize event is inherited from the Ext.dom.Element resize event.
The params list there are described as follows (not including eOpts)
* @param {Ext.dom.Element} this The component instance.
* @param {Object} info The element's new size parameters.
This suggest that the first parameter is a subclass of Ext.dom.Element (which is not the case for Ext.Component).

Even worse: This suggest that the second parameter is a JS object that contains all the size values.
This is also not the case for Ext.Component (I haven't tested if this applies to Ext.dom.Element).

There are 4 more parameters that get passed to the resize event handler.
Their types are as follows: [ Ext.Component, int, int, int, int, object, object]

As far as I can tell the full parameters list for the Ext.Component.resize event are as follows (be aware: could be slightly wrong)
* @param {Ext.Component} this The component instance.
* @param {Number} width The element's new width.
* @param {Number} height The element's new height.
* @param {Number} oldWidth The element's old width.
* @param {Number} oldHeight The element's old height.
* @param {Object} info The element's new size parameters.
* @param {Object} eOpts The options object passed to Ext.util.Observable.addListener.