Use PluginPrefs in ChromePluginServiceFilter to check whether a plugin is enabled.

content/common/content_notification_types.h

 // Copyright (c) 2011 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 CONTENT_COMMON_NOTIFICATION_TYPE_H_
 #define CONTENT_COMMON_NOTIFICATION_TYPE_H_
 #pragma once
 
 // This file describes various types used to describe and filter notifications
 // that pass through the NotificationService.
@@ skipping 393 matching lines @@
   // This message indicates that an instance of a particular child was
   // created in a page.  (If one page contains several regions rendered by
   // the same child, this notification will occur once for each region
   // during the page load.)
   //
   // There is no usable source, since it is sent from an ephemeral task;
   // register for AllSources() to receive this notification.  The details are
   // in a Details<ChildProcessInfo>.
   NOTIFICATION_CHILD_INSTANCE_CREATED,
 
-  // Sent by the PluginUpdater when there is a change of plugin
-  // enable/disable status.
-  NOTIFICATION_PLUGIN_ENABLE_STATUS_CHANGED,
-
   // Download Notifications --------------------------------------------------
 
   // Sent when a page generation to MHTML has finished.
   // The source is the corresponding RenderViewHost. The details is a
   // MHTMLGenerationManager::NotificationDetails.
   NOTIFICATION_MHTML_GENERATED,
 
   // Saved Pages -------------------------------------------------------------
 
   // Sent when a SavePackage finishes successfully. The source is the
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   // of a temporary zoom level change, the details is an empty string.
   NOTIFICATION_ZOOM_LEVEL_CHANGED,
 
   // Custom notifications used by the embedder should start from here.
   NOTIFICATION_CONTENT_END,
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_NOTIFICATION_TYPE_H_