[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': [
     {
       '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.
@@ skipping 46 matching lines @@
         'forwarder.cc',
         'forwarders_manager.cc',
         'host_controller.cc',
         'host_forwarder_main.cc',
         'pipe_notifier.cc',
         'socket.cc',
       ],
     },
   ],
 }