Extract LazyBackgroundTaskQueue from ExtensionSystem.

extensions/browser/mock_extension_system.cc

 // Copyright 2014 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.
 
 #include "extensions/browser/mock_extension_system.h"
 
 #include "extensions/common/extension_set.h"
 
 namespace extensions {
 
@@ skipping 28 matching lines @@
 }
 
 StateStore* MockExtensionSystem::rules_store() {
   return nullptr;
 }
 
 InfoMap* MockExtensionSystem::info_map() {
   return nullptr;
 }
 
-LazyBackgroundTaskQueue* MockExtensionSystem::lazy_background_task_queue() {
-  return nullptr;
-}
-
 EventRouter* MockExtensionSystem::event_router() {
   return event_router_;
 }
 
 QuotaService* MockExtensionSystem::quota_service() {
   return nullptr;
 }
 
 const OneShotEvent& MockExtensionSystem::ready() const {
   return ready_;
 }
 
 ContentVerifier* MockExtensionSystem::content_verifier() {
   return nullptr;
 }
 
 scoped_ptr<ExtensionSet> MockExtensionSystem::GetDependentExtensions(
     const Extension* extension) {
   return scoped_ptr<ExtensionSet>();
 }
 
 }  // namespace extensions