Extract LazyBackgroundTaskQueue from ExtensionSystem.

extensions/shell/browser/shell_extension_system.h

Index: extensions/shell/browser/shell_extension_system.h
diff --git a/extensions/shell/browser/shell_extension_system.h b/extensions/shell/browser/shell_extension_system.h
index 3b5c122479d96facfc1ae4d94173c86555786efd..be1a4d4e2816362a89b05a80be2a7741c0baa59e 100644
--- a/extensions/shell/browser/shell_extension_system.h
+++ b/extensions/shell/browser/shell_extension_system.h
@@ -26,7 +26,6 @@ namespace extensions {
 class DeclarativeUserScriptManager;
 class EventRouter;
 class InfoMap;
-class LazyBackgroundTaskQueue;
 class ProcessManager;
 class RendererStartupHelper;
 class SharedUserScriptMaster;
@@ -61,7 +60,6 @@ class ShellExtensionSystem : public ExtensionSystem {
   StateStore* state_store() override;
   StateStore* rules_store() override;
   InfoMap* info_map() override;
-  LazyBackgroundTaskQueue* lazy_background_task_queue() override;
   EventRouter* event_router() override;
   InstallVerifier* install_verifier() override;
   QuotaService* quota_service() override;
@@ -82,7 +80,6 @@ class ShellExtensionSystem : public ExtensionSystem {
   scoped_refptr<InfoMap> info_map_;
 
   scoped_ptr<RuntimeData> runtime_data_;
-  scoped_ptr<LazyBackgroundTaskQueue> lazy_background_task_queue_;
   scoped_ptr<EventRouter> event_router_;
   scoped_ptr<QuotaService> quota_service_;