Re-add AC3/EAC3 audio demuxing support

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index abfa247f63c1c9da79cb492be741815cf0799582..35ba18db93402a767b7b5f69c381971838d08ac4 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1468,6 +1468,9 @@
     # Force disable libstdc++ debug mode.
     'disable_glibcxx_debug%': 0,
 
+    # Set to 1 to enable AC3/EAC3 audio demuxing
+    'enable_ac3_eac3_audio_demuxing%': 0,
+
     # Set to 1 to compile with MSE support for MPEG2 TS
     'enable_mpeg2ts_stream_parser%': 0,
 
@@ -1805,6 +1808,7 @@
         'use_system_fontconfig%': 1,
       }],
       ['chromecast==1', {
+        'enable_ac3_eac3_audio_demuxing%': 1,
         'enable_mpeg2ts_stream_parser%': 1,
         'ffmpeg_branding%': 'ChromeOS',
         'ozone_platform_ozonex%': 1,
@@ -2647,6 +2651,9 @@
           ['enable_mpeg2ts_stream_parser==1', {
             'defines': ['ENABLE_MPEG2TS_STREAM_PARSER'],
           }],
+          ['enable_ac3_eac3_audio_demuxing==1', {
+            'defines': ['ENABLE_AC3_EAC3_AUDIO_DEMUXING'],
+          }],
         ],
       }],
       ['enable_viewport==1', {