Refactor a bit.

service/taskqueue/interface.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 taskqueue
+
+// Interface is the full interface to the Task Queue service.
+type Interface interface {
+        Add(task *Task, queueName string) (*Task, error)
+        Delete(task *Task, queueName string) error
+
+        AddMulti(tasks []*Task, queueName string) ([]*Task, error)
+        DeleteMulti(tasks []*Task, queueName string) error
+
+        Lease(maxTasks int, queueName string, leaseTime int) ([]*Task, error)
+        LeaseByTag(maxTasks int, queueName string, leaseTime int, tag string) ([]*Task, error)
+        ModifyLease(task *Task, queueName string, leaseTime int) error
+
+        Purge(queueName string) error
+
+        QueueStats(queueNames []string) ([]Statistics, error)
+}