datastore: Add DecodeCursor to [Raw]Interface.

filter/count/rds.go

Index: filter/count/rds.go
diff --git a/filter/count/rds.go b/filter/count/rds.go
index f3ce9f8736cfbc22ecc544e62ad6db1d5bf4b4b7..5e40b6f758ec3752c4e338d15916443420b61a61 100644
--- a/filter/count/rds.go
+++ b/filter/count/rds.go
@@ -13,6 +13,7 @@ import (
 // DSCounter is the counter object for the datastore service.
 type DSCounter struct {
 	NewKey           Entry
+	DecodeCursor     Entry
 	DecodeKey        Entry
 	NewQuery         Entry
 	RunInTransaction Entry
@@ -45,6 +46,11 @@ func (r *dsCounter) NewQuery(kind string) ds.Query {
 	return r.ds.NewQuery(kind)
 }
 
+func (r *dsCounter) DecodeCursor(s string) (ds.Cursor, error) {
+	cursor, err := r.ds.DecodeCursor(s)
+	return cursor, r.c.DecodeCursor.up(err)
+}
+
 func (r *dsCounter) Run(q ds.Query, cb ds.RawRunCB) error {
 	return r.c.Run.up(r.ds.Run(q, cb))
 }