* Stub class for NetworkService-based URLRequest
* Create SimpleURLLoader
* Implement downloading
* Implement response event
* Only write data afte previous one finished
* Use DataPipeGetter for uploading data
* Support chunked upload data
* Call size callback at last
* Simplify UploadDataPipeGetter
* Implement cancelling and closing
* Handle redirection
* Fix uploading large data
* Emit error when request fails
* Emit error for redirection error
* Simplify emitting error
* "follow" should also emit "redirect" event
* SetLoadFlags is not really used
* Implement GetUploadProgress
* Implement FollowRedirect
* Fix exception with multiple redirections
* Reduce number of EmitEvent methods
* Emit response errors
* FetchRedirectMode => RedirectMode
