Add missing Count api

impl/dummy/dummy.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 dummy
 
 import (
         "fmt"
         "runtime"
         "strings"
@@ skipping 58 matching lines @@
 }
 func (ds) PutMulti([]*datastore.Key, []datastore.PropertyMap, datastore.PutMultiCB) error {
         panic(ni())
 }
 func (ds) GetMulti([]*datastore.Key, datastore.MultiMetaGetter, datastore.GetMultiCB) error {
         panic(ni())
 }
 func (ds) DeleteMulti([]*datastore.Key, datastore.DeleteMultiCB) error { panic(ni()) }
 func (ds) NewQuery(string) datastore.Query                             { panic(ni()) }
 func (ds) DecodeCursor(string) (datastore.Cursor, error)               { panic(ni()) }
+func (ds) Count(*datastore.FinalizedQuery) (int64, error)              { panic(ni()) }
 func (ds) Run(*datastore.FinalizedQuery, datastore.RawRunCB) error     { panic(ni()) }
 func (ds) RunInTransaction(func(context.Context) error, *datastore.TransactionOptions) error {
         panic(ni())
 }
 func (ds) Testable() datastore.Testable { return nil }
 
 var dummyDSInst = ds{}
 
 // Datastore returns a dummy datastore.RawInterface implementation suitable
 // for embedding. Every method panics with a message containing the name of the
@@ skipping 62 matching lines @@
 func (i) IsCapabilityDisabled(err error) bool                                      { panic(ni()) }
 func (i) IsOverQuota(err error) bool                                               { panic(ni()) }
 func (i) IsTimeoutError(err error) bool                                            { panic(ni()) }
 
 var dummyInfoInst = i{}
 
 // Info returns a dummy info.Interface implementation suitable for embedding.
 // Every method panics with a message containing the name of the method which
 // was unimplemented.
 func Info() info.Interface { return dummyInfoInst }