Introduce Dolby Vision video codec and Demuxer support

media/media_options.gni

Index: media/media_options.gni
diff --git a/media/media_options.gni b/media/media_options.gni
index b289851ab0f5aaebadb16eb4277c656b39092681..49948b84bf8fad1102e740035c2c014cd366b928 100644
--- a/media/media_options.gni
+++ b/media/media_options.gni
@@ -49,6 +49,12 @@ declare_args() {
   # platform. Enable by default for Chromecast.
   enable_hevc_demuxing = proprietary_codecs && is_chromecast
 
+  # Enable Dolby Vision demuxing. Enable by default for Chromecast. Actual
+  # decoding must be provided by the platform. Note some Dolby Vision profiles
+  # which are encoded using HEVC require |enable_hevc_demuxing| to be enabled.
+  enable_dolby_vision_demuxing =
+      proprietary_codecs && is_chromecast && !is_android
+
   enable_webrtc = !is_ios && !is_cast_audio_only
 
   # Enable HLS with SAMPLE-AES decryption.