Given a relative Uri and a base Uri, returns the absolute Uri of the relative Uri.
    
    
    
    
    
    
        
| Name | Type | Description | 
|---|---|---|
| relative | String | The relative Uri. | 
| base | String | optional The base Uri. | 
Returns:
    The absolute Uri of the given relative Uri.
        
    
    
Example:
//absolute Uri will be "https://test.com/awesome.png";
var absoluteUri = Cesium.getAbsoluteUri('awesome.png', 'https://test.com');