Parse FlexFEC RTP headers in Call and add integration with BWE.

webrtc/modules/congestion_controller/congestion_controller.cc

Index: webrtc/modules/congestion_controller/congestion_controller.cc
diff --git a/webrtc/modules/congestion_controller/congestion_controller.cc b/webrtc/modules/congestion_controller/congestion_controller.cc
index 44b2f41e86b85117b1e121ec6c56de1a028c29d4..9f38e5bf674b3d2dd1234c02db1b5e38e8f72d28 100644
--- a/webrtc/modules/congestion_controller/congestion_controller.cc
+++ b/webrtc/modules/congestion_controller/congestion_controller.cc
@@ -263,6 +263,17 @@ void CongestionController::EnablePeriodicAlrProbing(bool enable) {
   probe_controller_->EnablePeriodicAlrProbing(enable);
 }
 
+bool CongestionController::UseSendSideBwe(
+    bool transport_cc,
+    const RtpHeaderExtensionMap& rtp_header_extensions) {
+  // Has the RTCP feedback message been negotiated?
+  if (!transport_cc)
+    return false;
+  // Has the RTP header extension been negotiated?
+  return rtp_header_extensions.IsRegistered(
+      kRtpExtensionTransportSequenceNumber);
+}
+
 void CongestionController::SetAllocatedSendBitrateLimits(
     int min_send_bitrate_bps,
     int max_padding_bitrate_bps) {