proposal: x/net/context/ctxhttp: Context-aware HTTP handlers

[kyleconroy]

Proposal: add a context-aware handler interface that is similar to/mirrors http.Handler and http.HandlerFunc

type Handler interface {
    ServeHTTP(context.Context, http.ResponseWriter, *http.Request)
}

type HandlerFunc func(context.Context, http.ResponseWriter, *http.Request)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(c context.Context, w http.ResponseWriter, r *http.Request) {
    f(c, w, r)
}

In the future, we’d also want to add a ServerMux that implements the above interface. Thoughts?

[bradfitz]

This is a dup of rejected https://go-review.googlesource.com/#/c/15620/

Conversation continues in #13021 (moving context to std).