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

content/browser/plugin_process_host.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_BROWSER_PLUGIN_PROCESS_HOST_H_
 #define CONTENT_BROWSER_PLUGIN_PROCESS_HOST_H_
 #pragma once
 
 #include "build/build_config.h"
 
 #include <queue>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "content/browser/browser_child_process_host.h"
 #include "webkit/plugins/npapi/webplugininfo.h"
 #include "ui/gfx/native_widget_types.h"
 
+namespace content {
+class ResourceContext;
+}
+
 namespace gfx {
 class Rect;
 }
 
 namespace IPC {
 struct ChannelHandle;
 }
 
 class GURL;
 
 // Represents the browser side of the browser <--> plugin communication
 // channel.  Different plugins run in their own process, but multiple instances
 // of the same plugin run in the same process.  There will be one
 // PluginProcessHost per plugin process, matched with a corresponding
 // PluginProcess running in the plugin process.  The browser is responsible for
 // starting the plugin process when a plugin is created that doesn't already
 // have a process.  After that, most of the communication is directly between
 // the renderer and plugin processes.
 class PluginProcessHost : public BrowserChildProcessHost {
  public:
   class Client {
    public:
-    // Returns a opaque unique identifier for the process requesting
+    // Returns an opaque unique identifier for the process requesting
     // the channel.
     virtual int ID() = 0;
+    // Returns the resource context for the renderer requesting the channel.
+    virtual const content::ResourceContext& GetResourceContext() = 0;
     virtual bool OffTheRecord() = 0;
     virtual void SetPluginInfo(const webkit::npapi::WebPluginInfo& info) = 0;
     // The client should delete itself when one of these methods is called.
     virtual void OnChannelOpened(const IPC::ChannelHandle& handle) = 0;
     virtual void OnError() = 0;
 
    protected:
     virtual ~Client() {}
   };
 
@@ skipping 88 matching lines @@
   // Tracks modal windows currently visible.
   std::set<uint32> plugin_modal_windows_set_;
   // Tracks the current visibility of the cursor.
   bool plugin_cursor_visible_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(PluginProcessHost);
 };
 
 #endif  // CONTENT_BROWSER_PLUGIN_PROCESS_HOST_H_