Convert USE_PROPRIETARY_CODECS to a buildflag header.

media/cdm/aes_decryptor.cc

Index: media/cdm/aes_decryptor.cc
diff --git a/media/cdm/aes_decryptor.cc b/media/cdm/aes_decryptor.cc
index 8621584f3cc37dfdd3aa1ea4b779152c0342731b..83af9efd11a2a729af8d794f92cdd581fa7161ca 100644
--- a/media/cdm/aes_decryptor.cc
+++ b/media/cdm/aes_decryptor.cc
@@ -23,8 +23,9 @@
 #include "media/base/video_decoder_config.h"
 #include "media/base/video_frame.h"
 #include "media/cdm/json_web_key.h"
+#include "media/media_features.h"
 
-#if defined(USE_PROPRIETARY_CODECS)
+#if BUILDFLAG(USE_PROPRIETARY_CODECS)
 #include "media/cdm/cenc_utils.h"
 #endif
 
@@ -279,7 +280,7 @@ void AesDecryptor::CreateSessionAndGenerateRequest(
       keys.push_back(init_data);
       break;
     case EmeInitDataType::CENC:
-#if defined(USE_PROPRIETARY_CODECS)
+#if BUILDFLAG(USE_PROPRIETARY_CODECS)
       // |init_data| is a set of 0 or more concatenated 'pssh' boxes.
       if (!GetKeyIdsForCommonSystemId(init_data, &keys)) {
         promise->reject(CdmPromise::NOT_SUPPORTED_ERROR, 0,