PipeLine调用过程
ISAPIRuntime
ProcessReqeust
HttpRuntime
ProcessRequestNoDemand
ProcessRequestNow
ProcessRequestInternal
封装上下文
通过对象工厂获取application对象
HttpApplication
BeginProcessRequest
ResumeSteps
逐个执行步骤
StepManager
ResumeSteps
找到Derived Types
ApplicationStepManager
BuildSteps：向集合中加入注册事件处理程序
ResumeSteps
循环执行：application.ExecuteStep()

005-IIS处理过程