Re-add AC3/EAC3 audio demuxing support

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index 89e1ade22695a566e6b3fe11a4fe4a46eaab32ab..9eeb9ee140263ce62025e8dfd1e8025392536d66 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -33,9 +33,13 @@
       }, {
         'use_low_memory_buffer%': 0,
       }],
-      ['chromecast == 1', {
+      ['proprietary_codecs==1 and chromecast==1', {
+        # Enable AC3/EAC3 audio demuxing. Actual decoding must be provided by
+        # the platform (or HDMI sink in Chromecast for audio pass-through case).
+        'enable_ac3_eac3_audio_demuxing%': 1,
         'enable_mse_mpeg2ts_stream_parser%': 1,
       }, {
+        'enable_ac3_eac3_audio_demuxing%': 0,
         'enable_mse_mpeg2ts_stream_parser%': 0,
       }],
       ['chromecast==1', {
@@ -59,6 +63,7 @@
       'variables': {
         'buildflag_header_path': 'media/media_features.h',
         'buildflag_flags': [
+          "ENABLE_AC3_EAC3_AUDIO_DEMUXING=<(enable_ac3_eac3_audio_demuxing)",
           "ENABLE_MSE_MPEG2TS_STREAM_PARSER=<(enable_mse_mpeg2ts_stream_parser)",
         ],
       },