PreSendRequestHeaders and PreSendRequestContent should be fired when content is being sent

[twsouthwick]

If buffering is disabled and something is written. The framework HttpApplication will short circuit the request pipeline and jump to RequestNotification.SendReponse and raise PreSendRequestHeaders and PreSendRequestContent events.
In comparison systemweb-adapter will skip all the next stages and send the response.

HttpReponse.Flush() will expliexplicitly set RequestNotification = SendReponse. The StepManager will execute it. Following is the callstack.

>	System.Web.dll!System.Web.HttpContext.CurrentNotification.set(System.Web.RequestNotification **value = SendResponse**) Line 993	C#
 	System.Web.dll!System.Web.HttpRuntime.ProcessRequestNotificationPrivate(System.Web.Hosting.IIS7WorkerRequest wr, System.Web.HttpContext context) Line 1374	C#
 	System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(System.IntPtr rootedObjectsPointer, System.IntPtr nativeRequestContext, System.IntPtr moduleData, int flags) Line 461	C#
 	System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(System.IntPtr rootedObjectsPointer, System.IntPtr nativeRequestContext, System.IntPtr moduleData, int flags) Line 386	C#
 	[Native to Managed Transition]	
 	[Managed to Native Transition]	
 	System.Web.dll!System.Web.Hosting.IIS7WorkerRequest.ExplicitFlush() Line 1729	C#
 	System.Web.dll!System.Web.HttpResponse.Flush(bool finalFlush, bool async) Line 1238	C#
 	System.Web.dll!System.Web.HttpWriter.WriteFromStream(byte[] data, int offset, int size) Line 341	C#

Originally posted by @TaoziZ03 in #509 (comment)

[twsouthwick]

@TaoziZ03 do you need PreSendRequestContent ? We don't currently have that event enabled. If you do, please create a separate issue for it.

[twsouthwick]

@TaoziZ03 I have an implementation that should support PreSendRequestContent if you need it here: #515

[TaoziZ03]

Thanks! Yes, I need that. 👍