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

webrtc/modules/congestion_controller/include/congestion_controller.h

Index: webrtc/modules/congestion_controller/include/congestion_controller.h
diff --git a/webrtc/modules/congestion_controller/include/congestion_controller.h b/webrtc/modules/congestion_controller/include/congestion_controller.h
index 004a84752eefe4f063d06850519074fef2d4dd1a..98221796d59be2cd2cfb1da908ae93746d9ad964 100644
--- a/webrtc/modules/congestion_controller/include/congestion_controller.h
+++ b/webrtc/modules/congestion_controller/include/congestion_controller.h
@@ -22,6 +22,7 @@
 #include "webrtc/modules/pacing/packet_router.h"
 #include "webrtc/modules/pacing/paced_sender.h"
 #include "webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h"
+#include "webrtc/modules/rtp_rtcp/source/rtp_header_extension.h"
 
 namespace rtc {
 struct SentPacket;
@@ -88,6 +89,11 @@ class CongestionController : public CallStatsObserver, public Module {
   RateLimiter* GetRetransmissionRateLimiter();
   void EnablePeriodicAlrProbing(bool enable);
 
+  // Are the necessary RTCP and RTP header extensions enabled for send-side BWE?
+  static bool UseSendSideBwe(
+      bool transport_cc,
+      const RtpHeaderExtensionMap& rtp_header_extensions);
+
   // SetAllocatedSendBitrateLimits sets bitrates limits imposed by send codec
   // settings.
   // |min_send_bitrate_bps| is the total minimum send bitrate required by all