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

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 899c2c6a929a65b8e96c2e295a262f9fce563892..8522d5051d6dc7f5e98c26c8d945cb605a1780f0 100644
--- a/go/src/infra/gae/libs/meta/eg.go
+++ b/go/src/infra/gae/libs/meta/eg.go
@@ -7,11 +7,9 @@ package meta
 import (
 	"golang.org/x/net/context"
 
-	"appengine/datastore"
-
 	"github.com/luci/luci-go/common/errors"
 
-	"infra/gae/libs/wrapper"
+	"infra/gae/libs/gae"
 )
 
 var mark = errors.MakeMarkFn("eg")
@@ -20,24 +18,20 @@ var mark = errors.MakeMarkFn("eg")
 // appengine. You shouldn't need to use this struct directly, but instead should
 // use GetEntityGroupVersion.
 type EntityGroupMeta struct {
-	_kind string `datastore:"-" goon:"kind,__entity_group__"`
-
-	ID     int64          `datastore:"-" goon:"id"`
-	Parent *datastore.Key `datastore:"-" goon:"parent"`
-
-	Version int64 `datastore:"__version__"`
+	Version int64 `gae:"__version__"`
 }
 
 // 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.Context, root *datastore.Key) (int64, error) {
+func GetEntityGroupVersion(c context.Context, root gae.DSKey) (int64, error) {
 	for root.Parent() != nil {
 		root = root.Parent()
 	}
-	egm := &EntityGroupMeta{ID: 1, Parent: root}
-	err := wrapper.GetDS(c).Get(egm)
-	if err != datastore.ErrNoSuchEntity {
+	egm := &EntityGroupMeta{}
+	rds := gae.GetRDS(c)
+	err := rds.Get(rds.NewKey("__entity_group__", "", 1, root), egm)
+	if err != gae.ErrDSNoSuchEntity {
 		err = mark(err)
 	} else {
 		// this is OK for callers. The version of the entity group is effectively 0