Make udev target disappear on linux when use_udev==0

device/serial/serial.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': {
     'chromium_code': 1,
   },
   'targets': [
     {
       # GN version: //device/serial:serial_mojo
       'target_name': 'device_serial_mojo',
       # The type of this target must be none. This is so that resources can
       # depend upon this target for generating the js bindings files. Any
       # generated cpp files must be listed explicitly in device_serial
       'type': 'none',
       'includes': [
         '../../mojo/public/tools/bindings/mojom_bindings_generator.gypi',
       ],
       'sources': [
         'serial.mojom',
         'data_stream.mojom',
       ],
     },
     {
       # GN version: //device/serial
       'target_name': 'device_serial',
       'type': 'static_library',
       'conditions': [
-        ['OS=="linux"', {
+        ['use_udev == 1', {
           'dependencies': [
             '../../build/linux/system.gyp:udev',
           ],
+        }, {
+          'sources!': [
+            'serial_device_enumerator_linux.cc',
+            'serial_device_enumerator_linux.h',
+          ],
         }],
       ],
       'dependencies': [
         'device_serial_mojo',
         '../../mojo/mojo_base.gyp:mojo_cpp_bindings',
         '../../net/net.gyp:net',
       ],
       'export_dependent_settings': [
         'device_serial_mojo',
         '../../mojo/mojo_base.gyp:mojo_cpp_bindings',
@@ skipping 41 matching lines @@
         'device_serial',
         'device_serial_mojo',
       ],
       'sources': [
         'test_serial_io_handler.cc',
         'test_serial_io_handler.h',
       ],
     },
   ],
 }