Convert enable_mpeg2ts into a new-style buildflag

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index 3cbb74f7b085924244ff6a1e8978337f6b5c5961..0742b5a91069306751bcfb27c1053a583e5ac93b 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -48,10 +48,31 @@
   ],
   'targets': [
     {
+      # GN version: //media:media_features
+      'target_name': 'media_features',
+      'includes': [ '../build/buildflag_header.gypi' ],
+      'variables': {
+        'buildflag_header_path': 'media/media_features.h',
+        'variables': {
+          'conditions': [
+            ['chromecast == 1', {
+              'enable_mse_mpeg2ts_stream_parser%': 1,
+            }, {
+              'enable_mse_mpeg2ts_stream_parser%': 0,
+            }],
+          ],
+        },
+        'buildflag_flags': [
+          "ENABLE_MSE_MPEG2TS_STREAM_PARSER=<(enable_mse_mpeg2ts_stream_parser)",
+        ],
+      },
+    },
+    {
       # GN version: //media
       'target_name': 'media',
       'type': '<(component)',
       'dependencies': [
+        'media_features',
         '../base/base.gyp:base',
         '../base/base.gyp:base_i18n',
         '../base/third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',