Add missing Count api

impl/prod/raw_datastore.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 (
         ds "github.com/luci/gae/service/datastore"
         "github.com/luci/gae/service/info"
         "github.com/luci/luci-go/common/errors"
@@ skipping 164 matching lines @@
         }
 
         return ret, nil
 }
 
 func (d rdsImpl) DecodeCursor(s string) (ds.Cursor, error) {
         return datastore.DecodeCursor(s)
 }
 
 func (d rdsImpl) Run(fq *ds.FinalizedQuery, cb ds.RawRunCB) error {
-        tf := typeFilter{}
         q, err := d.fixQuery(fq)
         if err != nil {
                 return err
         }
 
         t := q.Run(d)
 
         cfunc := func() (ds.Cursor, error) {
                 return t.Cursor()
         }
+        tf := typeFilter{}
         for {
                 k, err := t.Next(&tf)
                 if err == datastore.Done {
                         return nil
                 }
                 if err != nil {
                         return err
                 }
                 if !cb(dsR2F(k), tf.pm, cfunc) {
                         return nil
                 }
         }
 }
 
+func (d rdsImpl) Count(fq *ds.FinalizedQuery) (int64, error) {
+        q, err := d.fixQuery(fq)
+        if err != nil {
+                return 0, err
+        }
+        ret, err := q.Count(d)
+        return int64(ret), err
+}
+
 func (d rdsImpl) RunInTransaction(f func(c context.Context) error, opts *ds.TransactionOptions) error {
         ropts := (*datastore.TransactionOptions)(opts)
         return datastore.RunInTransaction(d, f, ropts)
 }
 
 func (d rdsImpl) Testable() ds.Testable {
         return nil
 }