Better attempt at an appengine wrapper.

go/src/infra/gae/libs/meta/eg.go

Index: go/src/infra/gae/libs/meta/eg.go
diff --git a/go/src/infra/gae/libs/meta/eg.go b/go/src/infra/gae/libs/meta/eg.go
index 25463238fd8b095182a15a6524605d5ea0f34186..01e0f3eb4a06752039e5e7414ef02e5203aec904 100644
--- a/go/src/infra/gae/libs/meta/eg.go
+++ b/go/src/infra/gae/libs/meta/eg.go
@@ -2,16 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// +build appengine
-
 package meta
 
 import (
+	"golang.org/x/net/context"
+
 	"appengine/datastore"
 
 	"github.com/luci/luci-go/common/errors"
 
-	"infra/gae/libs/context"
+	"infra/gae/libs/wrapper"
 )
 
 var mark = errors.MakeMarkFn("eg")
@@ -31,12 +31,13 @@ type EntityGroupMeta struct {
 // GetEntityGroupVersion returns the entity group version for the entity group
 // containing root. If the entity group doesn't exist, this function will return
 // zero and a nil error.
-func GetEntityGroupVersion(c context.SingleReadWriter, root *datastore.Key) (int64, error) {
+func GetEntityGroupVersion(c context.Context, root *datastore.Key) (int64, error) {
+	ds := wrapper.GetDS(c)
 	for root.Parent() != nil {
 		root = root.Parent()
 	}
 	egm := &EntityGroupMeta{ID: 1, Parent: root}
-	err := c.Get(egm)
+	err := ds.Get(egm)
 	if err != datastore.ErrNoSuchEntity {
 		err = mark(err)
 	} else {