net/http: add new HTTP 451 status code, Unavailable For Legal Reasons.

Approved by the IETF.

https://datatracker.ietf.org/doc/draft-ietf-httpbis-legally-restricted-status/

Change-Id: I688597bb5f7ef7c7a9be660a4fcd2ef02d9dc9f4
Reviewed-on: https://go-review.googlesource.com/18112Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: David Symonds <dsymonds@golang.org>

src/net/http/status.go

@@ -47,6 +47,7 @@ const (
 	StatusPreconditionRequired         = 428
 	StatusTooManyRequests              = 429
 	StatusRequestHeaderFieldsTooLarge  = 431
+	StatusUnavailableForLegalReasons   = 451
 
 	StatusInternalServerError           = 500
 	StatusNotImplemented                = 501
@@ -99,6 +100,7 @@ var statusText = map[int]string{
 	StatusPreconditionRequired:         "Precondition Required",
 	StatusTooManyRequests:              "Too Many Requests",
 	StatusRequestHeaderFieldsTooLarge:  "Request Header Fields Too Large",
+	StatusUnavailableForLegalReasons:   "Unavailable For Legal Reasons",
 
 	StatusInternalServerError:           "Internal Server Error",
 	StatusNotImplemented:                "Not Implemented",