Add more components to the GN build.

components/plugins.gypi

 # 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.
 
 {
   'targets': [
     {
+      # GN version: //components/plugins/renderer
       'target_name': 'plugins_renderer',
       'type': 'static_library',
       'dependencies': [
         '../gin/gin.gyp:gin',
         '../skia/skia.gyp:skia',
         '../third_party/WebKit/public/blink.gyp:blink',
         '../third_party/re2/re2.gyp:re2',
         '../v8/tools/gyp/v8.gyp:v8',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'plugins/renderer/plugin_placeholder.cc',
         'plugins/renderer/plugin_placeholder.h',
         'plugins/renderer/webview_plugin.cc',
         'plugins/renderer/webview_plugin.h',
       ],
       'conditions' : [
         ['OS=="android"', {
           'sources': [
+            # Note: sources list duplicated in GN build.
             'plugins/renderer/mobile_youtube_plugin.cc',
             'plugins/renderer/mobile_youtube_plugin.h',
           ]
         }],
       ],
     },
   ]
 }