Add missing Count api

service/datastore/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 datastore
 
 import (
         "fmt"
         "reflect"
 
@@ skipping 90 matching lines @@
                 }
                 mat.setKey(itm, k)
                 return cbVal.Call([]reflect.Value{itm, reflect.ValueOf(gc)})[0].Bool()
         })
         if err == nil {
                 err = innerErr
         }
         return err
 }
 
+func (d *datastoreImpl) Count(q *Query) (int64, error) {
+        fq, err := q.Finalize()
+        if err != nil {
+                return 0, err
+        }
+        return d.RawInterface.Count(fq)
+}
+
 func (d *datastoreImpl) GetAll(q *Query, dst interface{}) error {
         v := reflect.ValueOf(dst)
         if v.Kind() != reflect.Ptr {
                 return fmt.Errorf("invalid GetAll dst: must have a ptr-to-slice: %T", dst)
         }
         if !v.IsValid() || v.IsNil() {
                 return errors.New("invalid GetAll dst: <nil>")
         }
 
         if keys, ok := dst.(*[]*Key); ok {
@@ skipping 137 matching lines @@
         err = lme.Get()
         if err == nil {
                 err = extErr
         }
         return
 }
 
 func (d *datastoreImpl) Raw() RawInterface {
         return d.RawInterface
 }