Extract LazyBackgroundTaskQueue from ExtensionSystem.

chrome/browser/extensions/extension_system_impl.h

Index: chrome/browser/extensions/extension_system_impl.h
diff --git a/chrome/browser/extensions/extension_system_impl.h b/chrome/browser/extensions/extension_system_impl.h
index 78c4cf64ca3bf2702e78756a54b7fca1ead22323..00a40f973dbebe467c382b57c20b29daf534e9c4 100644
--- a/chrome/browser/extensions/extension_system_impl.h
+++ b/chrome/browser/extensions/extension_system_impl.h
@@ -43,7 +43,6 @@ class ExtensionSystemImpl : public ExtensionSystem {
       override;                                                    // shared
   StateStore* state_store() override;                              // shared
   StateStore* rules_store() override;                              // shared
-  LazyBackgroundTaskQueue* lazy_background_task_queue() override;  // shared
   InfoMap* info_map() override;                                    // shared
   EventRouter* event_router() override;                            // shared
   InstallVerifier* install_verifier() override;
@@ -88,7 +87,6 @@ class ExtensionSystemImpl : public ExtensionSystem {
     SharedUserScriptMaster* shared_user_script_master();
     DeclarativeUserScriptManager* declarative_user_script_manager();
     InfoMap* info_map();
-    LazyBackgroundTaskQueue* lazy_background_task_queue();
     EventRouter* event_router();
     InstallVerifier* install_verifier();
     QuotaService* quota_service();
@@ -106,7 +104,6 @@ class ExtensionSystemImpl : public ExtensionSystem {
     scoped_ptr<StateStore> rules_store_;
     // LazyBackgroundTaskQueue is a dependency of
     // MessageService and EventRouter.
-    scoped_ptr<LazyBackgroundTaskQueue> lazy_background_task_queue_;
     scoped_ptr<EventRouter> event_router_;
     scoped_ptr<NavigationObserver> navigation_observer_;
     // Shared memory region manager for scripts statically declared in extension