[Android] Fix gn build for instrumentation tests.

tools/android/forwarder2/forwarder.gyp

 # Copyright (c) 2012 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: //tools/android/forwarder2
       'target_name': 'forwarder2',
       'type': 'none',
       'dependencies': [
         'device_forwarder',
         'host_forwarder#host',
       ],
       # For the component build, ensure dependent shared libraries are stripped
       # and put alongside forwarder to simplify pushing to the device.
       'variables': {
          'output_dir': '<(PRODUCT_DIR)/forwarder_dist/',
          'native_binary': '<(PRODUCT_DIR)/device_forwarder',
       },
       'includes': ['../../../build/android/native_app_dependencies.gypi'],
     },
     {
+      # GN version: //tools/android/forwarder2:device_forwarder
       'target_name': 'device_forwarder',
       'type': 'executable',
       'toolsets': ['target'],
       'dependencies': [
         '../../../base/base.gyp:base',
         '../../../build/android/pylib/device/commands/commands.gyp:chromium_commands',
         '../common/common.gyp:android_tools_common',
       ],
       'include_dirs': [
         '../../..',
       ],
       'sources': [
         'command.cc',
         'common.cc',
         'daemon.cc',
         'device_controller.cc',
         'device_forwarder_main.cc',
         'device_listener.cc',
         'forwarder.cc',
         'forwarders_manager.cc',
         'pipe_notifier.cc',
         'socket.cc',
       ],
     },
     {
+      # GN version: //tools/android/forwarder2:host_forwarder
       'target_name': 'host_forwarder',
       'type': 'executable',
       'toolsets': ['host'],
       'dependencies': [
         '../../../base/base.gyp:base',
         '../common/common.gyp:android_tools_common',
       ],
       'include_dirs': [
         '../../..',
       ],
       'sources': [
         'command.cc',
         'common.cc',
         'daemon.cc',
         'forwarder.cc',
         'forwarders_manager.cc',
         'host_controller.cc',
         'host_forwarder_main.cc',
         'pipe_notifier.cc',
         'socket.cc',
       ],
     },
   ],
 }