Merge MediaChannel's OnTransportOverheadChanged and OnNetworkRouteChanged callbacks.

OnTransportOverChanged is merged into OnNetworkRouteChanged in MediaChannel
because the transport overhead will be added to rtc::NetworkRoute structure.

This CL depends on https://webrtc-review.googlesource.com/c/src/+/13520

Bug: None
Change-Id: I6ed6583f6c91db4ce61a89406de39774239f3a04
Reviewed-on: https://webrtc-review.googlesource.com/15200
Commit-Queue: Zhi Huang <zhihuang@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Peter Thatcher <pthatcher@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20678}
diff --git a/media/base/fakemediaengine.h b/media/base/fakemediaengine.h
index e067c19..f0fae7b 100644
--- a/media/base/fakemediaengine.h
+++ b/media/base/fakemediaengine.h
@@ -273,14 +273,12 @@
   virtual void OnReadyToSend(bool ready) {
     ready_to_send_ = ready;
   }
-  virtual void OnTransportOverheadChanged(int transport_overhead_per_packet) {
-    transport_overhead_per_packet_ = transport_overhead_per_packet;
-  }
 
   virtual void OnNetworkRouteChanged(const std::string& transport_name,
                                      const rtc::NetworkRoute& network_route) {
     last_network_route_ = network_route;
     ++num_network_route_changes_;
+    transport_overhead_per_packet_ = network_route.packet_overhead;
   }
   bool fail_set_send_codecs() const { return fail_set_send_codecs_; }
   bool fail_set_recv_codecs() const { return fail_set_recv_codecs_; }