net/http: add method constants

Fixes #12078

Change-Id: Ia8738123b07ca29be4a0cf400ee143729c8b5b3c
Reviewed-on: https://go-review.googlesource.com/16860Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/method.go

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http
+
+// Common HTTP methods.
+//
+// Unless otherwise noted, these are defined in RFC 7231 section 4.3.
+const (
+	MethodGet     = "GET"
+	MethodHead    = "HEAD"
+	MethodPost    = "POST"
+	MethodPut     = "PUT"
+	MethodPatch   = "PATCH" // RFC 5741
+	MethodDelete  = "DELETE"
+	MethodConnect = "CONNECT"
+	MethodOptions = "OPTIONS"
+	MethodTrace   = "TRACE"
+)