title: IHttpAsyncHandler instance use by the runtime
body: <p>Given an IHttpAsyncHandler instance A, will A be the instance that receives the EndProcessRequest callback?  If so, it is guaranteed?  Does the IsReusable property alter the behavior at all?</p>
  
  <p>It's complicated enough to try to test that I wanted to reach out and see if someone else had already been down this road.</p>
  
  <p>I currently have a IHttpAsyncHandler that uses a state object that gets sent to EndProcessRequest and everything is working perfectly.  However, I could clean the code considerably if I could preserve state in an instance level variable like a property or field.</p>
  
  <p>Thoughts?</p>