Factor Google Now welcome notifications out of DesktopNotificationService.

chrome/browser/notifications/extension_welcome_notification_factory.h

+// 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.
+
+#ifndef CHROME_BROWSER_NOTIFICATIONS_EXTENSION_WELCOME_NOTIFICATION_FACTORY_H_
+#define CHROME_BROWSER_NOTIFICATIONS_EXTENSION_WELCOME_NOTIFICATION_FACTORY_H_
+
+#include "base/memory/singleton.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+
+class ExtensionWelcomeNotification;
+
+// Singleton owning the extension welcome notification objects and associates
+// them with the browser context for which they may have to be shown.
+class ExtensionWelcomeNotificationFactory
+    : public BrowserContextKeyedServiceFactory {
+ public:
+  // Returns the ExtensionWelcomeNotification instance to be used for |context|.
+  static ExtensionWelcomeNotification* GetForBrowserContext(
+      content::BrowserContext* context);
+
+  static ExtensionWelcomeNotificationFactory* GetInstance();
+
+ private:
+  friend struct DefaultSingletonTraits<ExtensionWelcomeNotificationFactory>;
+
+  ExtensionWelcomeNotificationFactory();
+  virtual ~ExtensionWelcomeNotificationFactory();
+
+  // BrowserContextKeyedServiceFactory:
+  virtual KeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* context) const OVERRIDE;
+  virtual content::BrowserContext* GetBrowserContextToUse(
+      content::BrowserContext* context) const OVERRIDE;
+};
+
+#endif  // CHROME_BROWSER_NOTIFICATIONS_EXTENSION_WELCOME_NOTIFICATION_FACTORY_H_