ReportCanvas.subscribeCanvasLoadedEvent Method
        
 Subscribe a handler to the canvasloaded event.
 
         
        Parameters
        
            - handler
            
 
            - 
                
Type: Function
The handler. 
            - unsubscribe
            
 
            - 
                
Type: Boolean - May be null
(Optional) True to unsubscribe. 
            - once
            
 
            - 
                
Type: Boolean - May be null
(Optional) True to run handler once only.