Improve docs

impl/prod/context.go

 // Copyright 2015 The Chromium 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 prod
 
 import (
+        "net/http"
+
         "golang.org/x/net/context"
+        "google.golang.org/appengine"
 )
 
-// Use adds production implementations for all the gae services to the context.
+// Use adds production implementations for all the gae services to the context,
+// using the existing context obtained by appengine.NewContext.
 //
 // The services added are:
 //   - github.com/luci/gae/service/rawdatastore
 //   - github.com/luci/gae/service/taskqueue
 //   - github.com/luci/gae/service/memcache
 //   - github.com/luci/gae/service/info
 //
 // These can be retrieved with the <service>.Get functions.
 //
 // The implementations are all backed by the real appengine SDK functionality,
 func Use(c context.Context) context.Context {
         return useRDS(useMC(useTQ(useGI(c))))
 }
+
+// Use adds production implementations for all the gae services to the context.
+//
+// The services added are:
+//   - github.com/luci/gae/service/rawdatastore
+//   - github.com/luci/gae/service/taskqueue
+//   - github.com/luci/gae/service/memcache
+//   - github.com/luci/gae/service/info
+//
+// These can be retrieved with the <service>.Get functions.
+//
+// The implementations are all backed by the real appengine SDK functionality,
+func UseRequest(r *http.Request) context.Context {
+        return useRDS(useMC(useTQ(useGI(appengine.NewContext(r)))))
+}