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

chrome/chrome_browser.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'dependencies': [
@@ skipping 326 matching lines @@
         '<(protoc_out_dir)/chrome/browser/userfeedback/proto/math.pb.cc',
         '<(protoc_out_dir)/chrome/browser/userfeedback/proto/web.pb.cc',
         'browser/character_encoding.cc',
         'browser/character_encoding.h',
         'browser/chrome_browser_application_mac.h',
         'browser/chrome_browser_application_mac.mm',
         'browser/chrome_content_browser_client.cc',
         'browser/chrome_content_browser_client.h',
         'browser/chrome_plugin_message_filter.cc',
         'browser/chrome_plugin_message_filter.h',
+        'browser/chrome_plugin_service_filter.cc',
+        'browser/chrome_plugin_service_filter.h',
         'browser/chrome_quota_permission_context.cc',
         'browser/chrome_quota_permission_context.h',
         'browser/chrome_worker_message_filter.cc',
         'browser/chrome_worker_message_filter.h',
         'browser/chromeos/accessibility_util.cc',
         'browser/chromeos/accessibility_util.h',
         'browser/chromeos/audio_handler.cc',
         'browser/chromeos/audio_handler.h',
         'browser/chromeos/audio_mixer.h',
         'browser/chromeos/audio_mixer_alsa.cc',
@@ skipping 4581 matching lines @@
               # weak imports in dependents, who still must #include
               # closure_blocks_leopard_compat.h to get weak imports.
               'type': 'none',
             }],
           ],
         },
       ],
     }],
   ],
 }