Change frame length on very low bandwidth.

webrtc/modules/audio_coding/audio_network_adaptor/frame_length_controller.h

Index: webrtc/modules/audio_coding/audio_network_adaptor/frame_length_controller.h
diff --git a/webrtc/modules/audio_coding/audio_network_adaptor/frame_length_controller.h b/webrtc/modules/audio_coding/audio_network_adaptor/frame_length_controller.h
index fa6e753b34e414c59459741380e02e8301ec1c32..74cbb5638d7df61531b668e3bdbd67fa1a0fd935 100644
--- a/webrtc/modules/audio_coding/audio_network_adaptor/frame_length_controller.h
+++ b/webrtc/modules/audio_coding/audio_network_adaptor/frame_length_controller.h
@@ -32,6 +32,7 @@ class FrameLengthController final : public Controller {
     };
     Config(const std::vector<int>& encoder_frame_lengths_ms,
            int initial_frame_length_ms,
+           int min_encoder_bitrate_bps,
            float fl_increasing_packet_loss_fraction,
            float fl_decreasing_packet_loss_fraction,
            std::map<FrameLengthChange, int> fl_changing_bandwidths_bps);
@@ -39,6 +40,7 @@ class FrameLengthController final : public Controller {
     ~Config();
     std::vector<int> encoder_frame_lengths_ms;
     int initial_frame_length_ms;
+    int min_encoder_bitrate_bps;
     // Uplink packet loss fraction below which frame length can increase.
     float fl_increasing_packet_loss_fraction;
     // Uplink packet loss fraction below which frame length should decrease.
@@ -69,6 +71,8 @@ class FrameLengthController final : public Controller {
 
   rtc::Optional<float> uplink_packet_loss_fraction_;
 
+  rtc::Optional<size_t> overhead_bytes_per_packet_;
+
   RTC_DISALLOW_COPY_AND_ASSIGN(FrameLengthController);
 };