Bugzilla

As for how [VideoCodec::startBitrate](https://searchfox.org/mozilla-central/rev/6c8d325e61b0b445ed2e04899da38c3a4c266cba/third_party/libwebrtc/api/video_codecs/video_codec.h#113) is used by our code, we use it in [WebrtcGmpVideoEncoder::InitEncode](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/webrtc/libwebrtcglue/WebrtcGmpVideoCodec.cpp#138) and [WebrtcMediaDataEncoder::SetupConfig](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/webrtc/libwebrtcglue/WebrtcMediaDataEncoderCodec.cpp#193).

As for how [VideoCodec::startBitrate](https://searchfox.org/mozilla-central/rev/6c8d325e61b0b445ed2e04899da38c3a4c266cba/third_party/libwebrtc/api/video_codecs/video_codec.h#113) is used by our code, we pass it to:
* [WebrtcGmpVideoEncoder::InitEncode](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/webrtc/libwebrtcglue/WebrtcGmpVideoCodec.cpp#138), but I do not see anyplace where it is actually used, and
* [WebrtcMediaDataEncoder::SetupConfig](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/webrtc/libwebrtcglue/WebrtcMediaDataEncoderCodec.cpp#193), which is passed to [BitrateAdjuster::SetTargetBitrateBps](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/third_party/libwebrtc/common_video/bitrate_adjuster.cc#41,55,57) to update [BitrateAdjuster::target_bitrate_bps_ (and maybe BitrateAdjuster::adjusted_bitrate_bps_ and BitrateAdjuster::last_adjusted_target_bitrate_bps_)](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/third_party/libwebrtc/common_video/bitrate_adjuster.cc#41,55,57), which is then used in [WebrtcMediaDataEncoder::CreateEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/webrtc/libwebrtcglue/WebrtcMediaDataEncoderCodec.cpp#230), which then ends up in either:
    * [MediaDataEncoder::H264Config](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/PlatformEncoderModule.h#343-345), which is used to configure either an [AndroidDataEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/android/AndroidEncoderModule.cpp#35), an [AppleVTEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/apple/AppleEncoderModule.cpp#21), or a [WMFMediaDataEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/wmf/WMFEncoderModule.cpp#26)
    * [MediaDataEncoder::VP8Config](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/PlatformEncoderModule.h#357-359), which is used to configure an [AndroidDataEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/android/AndroidEncoderModule.cpp#39) or a [WMFMediaDataEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/wmf/WMFEncoderModule.cpp#30)
    * [MediaDataEncoder::VP9Config](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/PlatformEncoderModule.h#370-372), which is used to configure an [AndroidDataEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/android/AndroidEncoderModule.cpp#43) or a [WMFMediaDataEncoder](https://searchfox.org/mozilla-central/rev/a48e21143960b383004afa9ff9411c5cf6d5a958/dom/media/platforms/wmf/WMFEncoderModule.cpp#33)