ExtensionService.getExtensionFileUrl Method
        
 Gets the URL that should be used when installing an extension.
 
         
        Parameters
        
            - extensionPackageId
            
 
            - 
                
Type: String
(optional) The ID of the extension package if one is being downloaded.
Optional: True 
        
        Return Value
        
Type: String
        
The URL that can be used for a file upload.