Fix V4L2VideoEncodeAccelerator is not enabled in GN build

media/gpu/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")
 import("//build/config/ui.gni")
 import("//media/gpu/args.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
@@ skipping 113 matching lines @@
 
     args += rebase_path(sources, root_build_dir)
   }
 }
 
 config("gpu_config") {
   defines = []
   if (is_chromeos && use_v4lplugin) {
     defines += [ "USE_LIBV4L2" ]
   }
+  if (is_chromeos && use_v4l2_codec) {
+    defines += [ "USE_V4L2_CODEC" ]
+  }
 }
 
 component("gpu") {
   output_name = "media_gpu"
 
   # Only local test code, GPU-related IPC code in the media layer, and
   # media-related content code should access //media/gpu.
   visibility = [
     "//content/gpu:*",
     "//content/public/gpu:*",
@@ skipping 106 matching lines @@
       "vp9_decoder.cc",
       "vp9_decoder.h",
       "vp9_picture.cc",
       "vp9_picture.h",
     ]
     if (use_v4lplugin) {
       sources += get_target_outputs(":libv4l2_generate_stubs")
       deps += [ ":libv4l2_generate_stubs" ]
     }
     if (use_v4l2_codec) {
-      defines += [ "USE_V4L2_CODEC" ]
       deps += [ "//third_party/libyuv" ]
       sources += [
         "generic_v4l2_device.cc",
         "generic_v4l2_device.h",
         "v4l2_device.cc",
         "v4l2_device.h",
         "v4l2_image_processor.cc",
         "v4l2_image_processor.h",
         "v4l2_jpeg_decode_accelerator.cc",
         "v4l2_jpeg_decode_accelerator.h",
@@ skipping 183 matching lines @@
       "video_encode_accelerator_unittest.cc",
     ]
     if (use_x11) {
       deps += [ "//ui/gfx/x" ]
     }
     if (use_ozone) {
       deps += [ "//ui/ozone" ]
     }
   }
 }