To M56: Fix mimetype mappings for FLAC support.

media/base/mime_util_internal.cc

Index: media/base/mime_util_internal.cc
diff --git a/media/base/mime_util_internal.cc b/media/base/mime_util_internal.cc
index 11a763e74ab3c0054e6a39db8a3bcdbac462b19b..9c052c5c0803049fac547150769460cefe665a20 100644
--- a/media/base/mime_util_internal.cc
+++ b/media/base/mime_util_internal.cc
@@ -408,6 +408,7 @@ void MimeUtil::AddSupportedMediaFormats() {
     AddContainerWithCodecs("video/ogg", ogg_codecs, false);
   // TODO(ddorwin): Should the application type support Opus?
   AddContainerWithCodecs("application/ogg", ogg_codecs, false);
+  AddContainerWithCodecs("audio/flac", implicit_codec, false);
 
 #if defined(USE_PROPRIETARY_CODECS)
   AddContainerWithCodecs("audio/mpeg", mp3_codecs, true);  // Allow "mp3".
@@ -565,6 +566,7 @@ bool MimeUtil::IsCodecSupportedOnPlatform(
     case PCM:
     case MP3:
     case MPEG4_AAC:
+    case FLAC:
     case VORBIS:
       // These codecs are always supported; via a platform decoder (when used
       // with MSE/EME), a software decoder (the unified pipeline), or with
@@ -769,6 +771,7 @@ bool MimeUtil::IsCodecProprietary(Codec codec) const {
     case PCM:
     case VORBIS:
     case OPUS:
+    case FLAC:
     case VP8:
     case VP9:
     case THEORA:
@@ -792,6 +795,11 @@ bool MimeUtil::GetDefaultCodecLowerCase(const std::string& mime_type_lower_case,
     return true;
   }
 
+  if (mime_type_lower_case == "audio/flac") {
+    *default_codec = MimeUtil::FLAC;
+    return true;
+  }
+
   return false;
 }