Reland: Refactor current GAE abstraction library to be free of the SDK*

go/src/infra/gae/libs/wrapper/gae/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 gae
-
-import (
-        "errors"
-        "golang.org/x/net/context"
-
-        "appengine"
-
-        "github.com/mjibson/goon"
-)
-
-// Use adds implementations for the following gae/wrapper interfaces to the
-// context:
-//   * wrapper.Datastore
-//   * wrapper.TaskQueue
-//   * wrapper.Memcache
-//   * wrapper.GlobalInfo
-//
-// These can be retrieved with the "gae/wrapper".Get functions.
-//
-// The implementations are all backed by the real "appengine" SDK functionality,
-// and by "github.com/mjibson/goon".
-//
-// Using this more than once per context.Context will cause a panic.
-func Use(c context.Context, gaeCtx appengine.Context) context.Context {
-        if c.Value(goonContextKey) != nil {
-                panic(errors.New("gae.Use: called twice on the same Context"))
-        }
-        c = context.WithValue(c, goonContextKey, goon.FromContext(gaeCtx))
-        return useDS(useMC(useTQ(useGI(c))))
-}
-
-type key int
-
-var goonContextKey key
-
-func ctx(c context.Context) *goon.Goon {
-        return c.Value(goonContextKey).(*goon.Goon)
-}