Content-Length using UpdatePanels in Chrome

I have this error in Chrome

http://stackoverflow.com/questions/37434368/failed-to-load-resource-neterr-incomplete-chunked-encoding-in-ie-asp-net

Maybe can be problems with Content-Length in Chrome using UpdatePanels. I don't know. (searching forums googling)

For example, using AJAX (XMLHttpRequest), I can use like this:

xmlHttp=new XMLHttpRequest();     
xmlHttp.setRequestHeader('If-Modified-Since', 'Sat, 1 Jan 2000 00:00:00 GMT');     
xmlHttp.setRequestHeader('Content-Type','application/x-www-form-urlencoded; charset=UTF-8');    

 xmlHttp.setRequestHeader('Content-length', sc.length);

Using Update Panels (AjaxControlToolkit), I have this object, and events InitializeRequest, BeginRequest, ... but I don't know how-to set 'Content-length' value.

var prm = Sys.WebForms.PageRequestManager.getInstance();      

prm.add_initializeRequest(InitializeRequest);      

prm.add_beginRequest(BeginRequest);

Any suggestions for troubleshooting ?