Inline extensions .gypi files into GN build.

extensions/components/extensions_components.gyp

-# Copyright 2014 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.
-
-{
-  'variables': {
-    # This turns on e.g. the filename-based detection of which
-    # platforms to include source files on (e.g. files ending in
-    # _mac.h or _mac.cc are only compiled on MacOSX).
-    'chromium_code': 1,
-  },
-  'includes': [
-    'javascript_dialog_extensions_client.gypi',
-  ],
-  'conditions': [
-    ['toolkit_views==1', {
-      'includes': [
-        'native_app_window.gypi',
-      ],
-    }],
-  ],
-}