在尝试解决为什么chrome没有使用文件的缓存版本时，在chrome：// net-internals /＃events中看到net_error = -2错误，是否知道-2代码意味着什么？
t=113683 [st= 0] URL_REQUEST_DELEGATE [dt=0]
t=113684 [st= 1] HTTP_CACHE_GET_BACKEND [dt=0]
t=113684 [st= 1] HTTP_CACHE_OPEN_ENTRY [dt=1]
--> net_error = -2 (ERR_FAILED)
t=113685 [st= 2] HTTP_CACHE_CREATE_ENTRY [dt=2]
t=113687 [st= 4] HTTP_CACHE_ADD_TO_ENTRY [dt=0]
t=113687 [st= 4] URL_REQUEST_DELEGATE [dt=0]
t=113687 [st= 4] +HTTP_STREAM_REQUEST [dt=3]
t=113690 [st= 7] HTTP_STREAM_REQUEST_BOUND_TO_JOB
--> source_dependency = 57257 (HTTP_STREAM_JOB)
t=113690 [st= 7] -HTTP_STREAM_REQUEST
t=113690 [st= 7] +HTTP_TRANSACTION_SEND_REQUEST [dt=0]