Extract LazyBackgroundTaskQueue from ExtensionSystem.

extensions/browser/lazy_background_task_queue.h

 // Copyright 2013 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.
 
 #ifndef EXTENSIONS_BROWSER_LAZY_BACKGROUND_TASK_QUEUE_H_
 #define EXTENSIONS_BROWSER_LAZY_BACKGROUND_TASK_QUEUE_H_
 
 #include <map>
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/linked_ptr.h"
 #include "base/scoped_observer.h"
+#include "components/keyed_service/core/keyed_service.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "extensions/browser/extension_registry_observer.h"
 
 namespace content {
 class BrowserContext;
 }
 
 namespace extensions {
 class Extension;
 class ExtensionHost;
 class ExtensionRegistry;
 
 // This class maintains a queue of tasks that should execute when an
 // extension's lazy background page is loaded. It is also in charge of loading
 // the page when the first task is queued.
 //
 // It is the consumer's responsibility to use this class when appropriate, i.e.
 // only with extensions that have not-yet-loaded lazy background pages.
-class LazyBackgroundTaskQueue : public content::NotificationObserver,
+class LazyBackgroundTaskQueue : public KeyedService,
+                                public content::NotificationObserver,
                                 public ExtensionRegistryObserver {
  public:
   typedef base::Callback<void(ExtensionHost*)> PendingTask;
 
   explicit LazyBackgroundTaskQueue(content::BrowserContext* browser_context);
   ~LazyBackgroundTaskQueue() override;
 
+  // Convenience method to return the LazyBackgroundTaskQueue for a given
+  // |context|.
+  static LazyBackgroundTaskQueue* Get(content::BrowserContext* context);
+
   // Returns the number of extensions having pending tasks.
   size_t extensions_with_pending_tasks() { return pending_tasks_.size(); }
 
   // Returns true if the task should be added to the queue (that is, if the
   // extension has a lazy background page that isn't ready yet). If the
   // extension has a lazy background page that is being suspended this method
   // cancels that suspension.
   bool ShouldEnqueueTask(content::BrowserContext* context,
                          const Extension* extension);
 
@@ skipping 39 matching lines @@
   content::NotificationRegistrar registrar_;
   PendingTasksMap pending_tasks_;
 
   ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
       extension_registry_observer_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_LAZY_BACKGROUND_TASK_QUEUE_H_