Don't use libvpx if it is disabled in GN build

media/cast/BUILD.gn

 # 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.
 
 component("cast") {
   deps = [
     ":sender",
     ":receiver",
   ]
 }
@@ skipping 90 matching lines @@
   ]
 
   deps = [
     ":common",
   ]
 }
 
 source_set("sender") {
   sources = [
     "cast_sender.h",
-# TODO(hclam): libvpx support.
-#    "cast_sender_impl.cc",
+    "cast_sender_impl.cc",
     "cast_sender_impl.h",
     "sender/audio_encoder.h",
     "sender/audio_encoder.cc",
     "sender/audio_sender.h",
     "sender/audio_sender.cc",
     "sender/congestion_control.h",
     "sender/congestion_control.cc",
     "sender/external_video_encoder.h",
     "sender/external_video_encoder.cc",
     "sender/fake_software_video_encoder.h",
     "sender/fake_software_video_encoder.cc",
     "sender/frame_sender.cc",
     "sender/frame_sender.h",
     "sender/rtp_timestamp_helper.cc",
     "sender/rtp_timestamp_helper.h",
     "sender/software_video_encoder.h",
-# TODO(hclam): libvpx support.
-#    "sender/video_encoder.h",
-#    "sender/video_encoder_impl.h",
-#    "sender/video_encoder_impl.cc",
-#    "sender/video_sender.h",
-#    "sender/video_sender.cc",
+    "sender/video_encoder.h",
+    "sender/video_encoder_impl.h",
+    "sender/video_encoder_impl.cc",
+    "sender/video_sender.h",
+    "sender/video_sender.cc",
 #    "sender/vp8_encoder.cc",
 #    "sender/vp8_encoder.h",
   ]
 
   deps = [
     ":common",
     ":net",
     "//media",
     "//media:shared_memory_support",
     "//third_party/opus",
@@ skipping 171 matching lines @@
   sources = [
     "test/utility/udp_proxy_main.cc",
   ]
 
   deps = [
     ":test_support",
     "//base",
     "//net",
   ]
 }