[Extensions] Clean up renderer channel-related code

chrome/browser/extensions/chrome_notification_observer.cc

-// 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.
-
-#include "chrome/browser/extensions/chrome_notification_observer.h"
-
-#include "content/public/browser/notification_service.h"
-#include "content/public/browser/notification_types.h"
-#include "content/public/browser/render_process_host.h"
-#include "extensions/common/extension_messages.h"
-#include "extensions/common/features/feature_channel.h"
-
-namespace extensions {
-
-ChromeNotificationObserver::ChromeNotificationObserver() {
-  registrar_.Add(this,
-                 content::NOTIFICATION_RENDERER_PROCESS_CREATED,
-                 content::NotificationService::AllBrowserContextsAndSources());
-}
-
-ChromeNotificationObserver::~ChromeNotificationObserver() {}
-
-void ChromeNotificationObserver::OnRendererProcessCreated(
-    content::RenderProcessHost* process) {
-  // Extensions need to know the channel for API restrictions. Send the channel
-  // to all renderers, as the non-extension renderers may have content scripts.
-  process->Send(
-      new ExtensionMsg_SetChannel(static_cast<int>(GetCurrentChannel())));
-}
-
-void ChromeNotificationObserver::Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) {
-  DCHECK_EQ(content::NOTIFICATION_RENDERER_PROCESS_CREATED, type);
-
-  OnRendererProcessCreated(
-      content::Source<content::RenderProcessHost>(source).ptr());
-}
-
-}  // namespace extensions