Do not register bandwidth observer for receive only channels.
An incoming rtcp report block is inserted to both send and receive channels in Call::DeliverRtcp. The report block may also be accepted by each receive channel (in addition to the send channel) but fails to calculate the rtt (=0).
Remove registration of bandwidth observer for receive channels. Prevents multiple callbacks to the bitrate controller (and with incorrect rtt) for an incoming report block.

BUG=4546
R=mflodman@webrtc.org, pbos@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45209004

Cr-Commit-Position: refs/heads/master@{#9055}
diff --git a/webrtc/video_engine/vie_channel.cc b/webrtc/video_engine/vie_channel.cc
index 3b467fb..557f14d 100644
--- a/webrtc/video_engine/vie_channel.cc
+++ b/webrtc/video_engine/vie_channel.cc
@@ -1853,7 +1853,6 @@
   configuration.audio = false;
   configuration.outgoing_transport = &vie_sender_;
   configuration.intra_frame_callback = intra_frame_observer_;
-  configuration.bandwidth_callback = bandwidth_observer_.get();
   configuration.rtt_stats = rtt_stats_;
   configuration.rtcp_packet_type_counter_observer =
       &rtcp_packet_type_counter_observer_;
@@ -1861,6 +1860,8 @@
   configuration.send_bitrate_observer = &send_bitrate_observer_;
   configuration.send_frame_count_observer = &send_frame_count_observer_;
   configuration.send_side_delay_observer = &send_side_delay_observer_;
+  if (sender_)
+    configuration.bandwidth_callback = bandwidth_observer_.get();
 
   return configuration;
 }