Extract LazyBackgroundTaskQueue from ExtensionSystem.

extensions/browser/lazy_background_task_queue.cc

Index: extensions/browser/lazy_background_task_queue.cc
diff --git a/extensions/browser/lazy_background_task_queue.cc b/extensions/browser/lazy_background_task_queue.cc
index b76b6d36743746c7650e670b99d0e2d9a46949e2..fcbde098967835801c2d4cc1e13e17c6c824ad76 100644
--- a/extensions/browser/lazy_background_task_queue.cc
+++ b/extensions/browser/lazy_background_task_queue.cc
@@ -14,6 +14,7 @@
 #include "extensions/browser/extension_host.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extensions_browser_client.h"
+#include "extensions/browser/lazy_background_task_queue_factory.h"
 #include "extensions/browser/notification_types.h"
 #include "extensions/browser/process_manager.h"
 #include "extensions/browser/process_map.h"
@@ -39,6 +40,12 @@ LazyBackgroundTaskQueue::LazyBackgroundTaskQueue(
 LazyBackgroundTaskQueue::~LazyBackgroundTaskQueue() {
 }
 
+// static
+LazyBackgroundTaskQueue* LazyBackgroundTaskQueue::Get(
+    content::BrowserContext* browser_context) {
+  return LazyBackgroundTaskQueueFactory::GetForBrowserContext(browser_context);
+}
+
 bool LazyBackgroundTaskQueue::ShouldEnqueueTask(
     content::BrowserContext* browser_context,
     const Extension* extension) {