Convert USE_PROPRIETARY_CODECS to a buildflag header.

media/cast/sender/h264_vt_encoder_unittest.cc

Index: media/cast/sender/h264_vt_encoder_unittest.cc
diff --git a/media/cast/sender/h264_vt_encoder_unittest.cc b/media/cast/sender/h264_vt_encoder_unittest.cc
index a91feed46a790d62630bc551cfd5745f15d711d4..72ff6735224fac8df9486dc7ce4782c28cb611bf 100644
--- a/media/cast/sender/h264_vt_encoder_unittest.cc
+++ b/media/cast/sender/h264_vt_encoder_unittest.cc
@@ -30,6 +30,7 @@
 #include "media/ffmpeg/ffmpeg_common.h"
 #include "media/filters/ffmpeg_glue.h"
 #include "media/filters/ffmpeg_video_decoder.h"
+#include "media/media_features.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
@@ -299,7 +300,7 @@ TEST_F(H264VideoToolboxEncoderTest, DISABLED_CheckFrameMetadataSequence) {
   EXPECT_EQ(10, metadata_recorder->count_frames_delivered());
 }
 
-#if defined(USE_PROPRIETARY_CODECS)
+#if BUILDFLAG(USE_PROPRIETARY_CODECS)
 // Failed on mac_chromium_rel_ng trybot. http://crbug.com/627260
 TEST_F(H264VideoToolboxEncoderTest, DISABLED_CheckFramesAreDecodable) {
   VideoDecoderConfig config(kCodecH264, H264PROFILE_MAIN, frame_->format(),