Add missing files in //device to appropriate BUILD.gn files.

device/gamepad/BUILD.gn

 # Copyright 2016 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.
 
 import("//build/config/features.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")  # For generate_jni().
 }
 
 component("gamepad") {
   output_name = "device_gamepad"
 
   sources = [
     "android/gamepad_jni_registrar.cc",
     "android/gamepad_jni_registrar.h",
     "game_controller_data_fetcher_mac.h",
     "game_controller_data_fetcher_mac.mm",
     "gamepad_consumer.cc",
     "gamepad_consumer.h",
     "gamepad_data_fetcher.cc",
     "gamepad_data_fetcher.h",
     "gamepad_data_fetcher_manager.cc",
     "gamepad_data_fetcher_manager.h",
+    "gamepad_export.h",
     "gamepad_monitor.cc",
     "gamepad_monitor.h",
     "gamepad_pad_state_provider.cc",
     "gamepad_pad_state_provider.h",
     "gamepad_platform_data_fetcher.h",
     "gamepad_platform_data_fetcher_android.cc",
     "gamepad_platform_data_fetcher_android.h",
     "gamepad_platform_data_fetcher_linux.cc",
     "gamepad_platform_data_fetcher_linux.h",
     "gamepad_platform_data_fetcher_mac.h",
@@ skipping 91 matching lines @@
     ]
     srcjar_deps = [ ":java_enums_srcjar" ]
   }
 
   java_cpp_enum("java_enums_srcjar") {
     sources = [
       "gamepad_standard_mappings.h",
     ]
   }
 }