clang-format produced code that (choose all that apply): 
- No sane human would ever choose

Here's the code before formatting:
// Wrapped to avoid static initializer startup cost.
const base::flat_map<std::string, MimeUtil::Codec>& GetStringToCodecMap() {
  static const base::flat_map<std::string, MimeUtil::Codec> kStringToCodecMap({
    // We only allow this for WAV so it isn't ambiguous.
    {"1", MimeUtil::PCM},
    // avc1/avc3.XXXXXX may be unambiguous; handled by ParseAVCCodecId().
    // hev1/hvc1.XXXXXX may be unambiguous; handled by ParseHEVCCodecID().
    // vp9, vp9.0, vp09.xx.xx.xx.xx.xx.xx.xx may be unambiguous; handled by
    // ParseVp9CodecID().
    {"mp3", MimeUtil::MP3},
    // Following is the list of RFC 6381 compliant audio codec strings:
    //   mp4a.66     - MPEG-2 AAC MAIN
    //   mp4a.67     - MPEG-2 AAC LC
    //   mp4a.68     - MPEG-2 AAC SSR
    //   mp4a.69     - MPEG-2 extension to MPEG-1 (MP3)
    //   mp4a.6B     - MPEG-1 audio (MP3)
    //   mp4a.40.2   - MPEG-4 AAC LC
    //   mp4a.40.02  - MPEG-4 AAC LC (leading 0 in aud-oti for compatibility)
    //   mp4a.40.5   - MPEG-4 HE-AAC v1 (AAC LC + SBR)
    //   mp4a.40.05  - MPEG-4 HE-AAC v1 (AAC LC + SBR) (leading 0 in aud-oti
    //                 for compatibility)
    //   mp4a.40.29  - MPEG-4 HE-AAC v2 (AAC LC + SBR + PS)
    {"mp4a.66", MimeUtil::MPEG2_AAC},
    {"mp4a.67", MimeUtil::MPEG2_AAC},
    {"mp4a.68", MimeUtil::MPEG2_AAC},
    {"mp4a.69", MimeUtil::MP3},
    {"mp4a.6B", MimeUtil::MP3},
    {"mp4a.40.2", MimeUtil::MPEG4_AAC},
    {"mp4a.40.02", MimeUtil::MPEG4_AAC},
    {"mp4a.40.5", MimeUtil::MPEG4_AAC},
    {"mp4a.40.05", MimeUtil::MPEG4_AAC},
    {"mp4a.40.29", MimeUtil::MPEG4_AAC},
#if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
    // TODO(servolk): Strictly speaking only mp4a.A5 and mp4a.A6 codec ids are
    // valid according to RFC 6381 section 3.3, 3.4. Lower-case oti (mp4a.a5
    // and mp4a.a6) should be rejected. But we used to allow those in older
    // versions of Chromecast firmware and some apps (notably MPL) depend on
    // those codec types being supported, so they should be allowed for now
    // (crbug.com/564960).
    {"ac-3", MimeUtil::AC3},
    {"mp4a.a5", MimeUtil::AC3},
    {"mp4a.A5", MimeUtil::AC3},
    {"ec-3", MimeUtil::EAC3},
    {"mp4a.a6", MimeUtil::EAC3},
    {"mp4a.A6", MimeUtil::EAC3},
#endif
    {"vorbis", MimeUtil::VORBIS},
    {"opus", MimeUtil::OPUS},
    {"flac", MimeUtil::FLAC},
    {"vp8", MimeUtil::VP8},
    {"vp8.0", MimeUtil::VP8},
    {"theora", MimeUtil::THEORA}
  }, base::KEEP_FIRST_OF_DUPES);

  return kStringToCodecMap;
}

Here's the code after formatting:
// Wrapped to avoid static initializer startup cost.
const base::flat_map<std::string, MimeUtil::Codec>& GetStringToCodecMap() {
  static const base::flat_map<std::string, MimeUtil::Codec> kStringToCodecMap(
      {
        // We only allow this for WAV so it isn't ambiguous.
        {"1", MimeUtil::PCM},
            // avc1/avc3.XXXXXX may be unambiguous; handled by
            // ParseAVCCodecId(). hev1/hvc1.XXXXXX may be unambiguous; handled
            // by ParseHEVCCodecID(). vp9, vp9.0, vp09.xx.xx.xx.xx.xx.xx.xx may
            // be unambiguous; handled by ParseVp9CodecID().
            {"mp3", MimeUtil::MP3},
            // Following is the list of RFC 6381 compliant audio codec strings:
            //   mp4a.66     - MPEG-2 AAC MAIN
            //   mp4a.67     - MPEG-2 AAC LC
            //   mp4a.68     - MPEG-2 AAC SSR
            //   mp4a.69     - MPEG-2 extension to MPEG-1 (MP3)
            //   mp4a.6B     - MPEG-1 audio (MP3)
            //   mp4a.40.2   - MPEG-4 AAC LC
            //   mp4a.40.02  - MPEG-4 AAC LC (leading 0 in aud-oti for
            //   compatibility) mp4a.40.5   - MPEG-4 HE-AAC v1 (AAC LC + SBR)
            //   mp4a.40.05  - MPEG-4 HE-AAC v1 (AAC LC + SBR) (leading 0 in
            //   aud-oti
            //                 for compatibility)
            //   mp4a.40.29  - MPEG-4 HE-AAC v2 (AAC LC + SBR + PS)
            {"mp4a.66", MimeUtil::MPEG2_AAC}, {"mp4a.67", MimeUtil::MPEG2_AAC},
            {"mp4a.68", MimeUtil::MPEG2_AAC}, {"mp4a.69", MimeUtil::MP3},
            {"mp4a.6B", MimeUtil::MP3}, {"mp4a.40.2", MimeUtil::MPEG4_AAC},
            {"mp4a.40.02", MimeUtil::MPEG4_AAC},
            {"mp4a.40.5", MimeUtil::MPEG4_AAC},
            {"mp4a.40.05", MimeUtil::MPEG4_AAC},
            {"mp4a.40.29", MimeUtil::MPEG4_AAC},
#if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
            // TODO(servolk): Strictly speaking only mp4a.A5 and mp4a.A6 codec
            // ids are valid according to RFC 6381 section 3.3, 3.4. Lower-case
            // oti (mp4a.a5 and mp4a.a6) should be rejected. But we used to
            // allow those in older versions of Chromecast firmware and some
            // apps (notably MPL) depend on those codec types being supported,
            // so they should be allowed for now (crbug.com/564960).
            {"ac-3", MimeUtil::AC3}, {"mp4a.a5", MimeUtil::AC3},
            {"mp4a.A5", MimeUtil::AC3}, {"ec-3", MimeUtil::EAC3},
            {"mp4a.a6", MimeUtil::EAC3}, {"mp4a.A6", MimeUtil::EAC3},
#endif
            {"vorbis", MimeUtil::VORBIS}, {"opus", MimeUtil::OPUS},
            {"flac", MimeUtil::FLAC}, {"vp8", MimeUtil::VP8},
            {"vp8.0", MimeUtil::VP8}, {
          "theora", MimeUtil::THEORA
        }
      },
      base::KEEP_FIRST_OF_DUPES);

  return kStringToCodecMap;
}

Here's how it ought to look:
// Wrapped to avoid static initializer startup cost.
const base::flat_map<std::string, MimeUtil::Codec>& GetStringToCodecMap() {
  static const base::flat_map<std::string, MimeUtil::Codec> kStringToCodecMap(
      {
        // We only allow this for WAV so it isn't ambiguous.
        {"1", MimeUtil::PCM},
        // avc1/avc3.XXXXXX may be unambiguous; handled by
        // ParseAVCCodecId(). hev1/hvc1.XXXXXX may be unambiguous; handled
        // by ParseHEVCCodecID(). vp9, vp9.0, vp09.xx.xx.xx.xx.xx.xx.xx may
        // be unambiguous; handled by ParseVp9CodecID().
        {"mp3", MimeUtil::MP3},
        // Following is the list of RFC 6381 compliant audio codec strings:
        //   mp4a.66     - MPEG-2 AAC MAIN
        //   mp4a.67     - MPEG-2 AAC LC
        //   mp4a.68     - MPEG-2 AAC SSR
        //   mp4a.69     - MPEG-2 extension to MPEG-1 (MP3)
        //   mp4a.6B     - MPEG-1 audio (MP3)
        //   mp4a.40.2   - MPEG-4 AAC LC
        //   mp4a.40.02  - MPEG-4 AAC LC (leading 0 in aud-oti for
        //   compatibility) mp4a.40.5   - MPEG-4 HE-AAC v1 (AAC LC + SBR)
        //   mp4a.40.05  - MPEG-4 HE-AAC v1 (AAC LC + SBR) (leading 0 in
        //   aud-oti
        //                 for compatibility)
        //   mp4a.40.29  - MPEG-4 HE-AAC v2 (AAC LC + SBR + PS)
        {"mp4a.66", MimeUtil::MPEG2_AAC}, {"mp4a.67", MimeUtil::MPEG2_AAC},
        {"mp4a.68", MimeUtil::MPEG2_AAC}, {"mp4a.69", MimeUtil::MP3},
        {"mp4a.6B", MimeUtil::MP3}, {"mp4a.40.2", MimeUtil::MPEG4_AAC},
        {"mp4a.40.02", MimeUtil::MPEG4_AAC},
        {"mp4a.40.5", MimeUtil::MPEG4_AAC},
        {"mp4a.40.05", MimeUtil::MPEG4_AAC},
        {"mp4a.40.29", MimeUtil::MPEG4_AAC},
#if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
        // TODO(servolk): Strictly speaking only mp4a.A5 and mp4a.A6 codec
        // ids are valid according to RFC 6381 section 3.3, 3.4. Lower-case
        // oti (mp4a.a5 and mp4a.a6) should be rejected. But we used to
        // allow those in older versions of Chromecast firmware and some
        // apps (notably MPL) depend on those codec types being supported,
        // so they should be allowed for now (crbug.com/564960).
        {"ac-3", MimeUtil::AC3}, {"mp4a.a5", MimeUtil::AC3},
        {"mp4a.A5", MimeUtil::AC3}, {"ec-3", MimeUtil::EAC3},
        {"mp4a.a6", MimeUtil::EAC3}, {"mp4a.A6", MimeUtil::EAC3},
#endif
        {"vorbis", MimeUtil::VORBIS}, {"opus", MimeUtil::OPUS},
        {"flac", MimeUtil::FLAC}, {"vp8", MimeUtil::VP8},
        {"vp8.0", MimeUtil::VP8}, {"theora", MimeUtil::THEORA},
      },
      base::KEEP_FIRST_OF_DUPES);

  return kStringToCodecMap;
}

Code review link for full files/context:
https://chromium-review.googlesource.com/c/584003/