Add support for transport wide sequence numbers

Also refactor packet router to use a map rather than iterate over all
rtp modules for each packet sent.

BUG=webrtc:4311

Review URL: https://codereview.webrtc.org/1247293002

Cr-Commit-Position: refs/heads/master@{#9670}

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc

@@ -30,19 +30,20 @@ RtpRtcp::Configuration::Configuration()
     : id(-1),
       audio(false),
       receiver_only(false),
-      clock(NULL),
+      clock(nullptr),
       receive_statistics(NullObjectReceiveStatistics()),
-      outgoing_transport(NULL),
-      intra_frame_callback(NULL),
-      bandwidth_callback(NULL),
-      rtt_stats(NULL),
-      rtcp_packet_type_counter_observer(NULL),
+      outgoing_transport(nullptr),
+      intra_frame_callback(nullptr),
+      bandwidth_callback(nullptr),
+      rtt_stats(nullptr),
+      rtcp_packet_type_counter_observer(nullptr),
       audio_messages(NullObjectRtpAudioFeedback()),
-      remote_bitrate_estimator(NULL),
-      paced_sender(NULL),
-      send_bitrate_observer(NULL),
-      send_frame_count_observer(NULL),
-      send_side_delay_observer(NULL) {
+      remote_bitrate_estimator(nullptr),
+      paced_sender(nullptr),
+      packet_router(nullptr),
+      send_bitrate_observer(nullptr),
+      send_frame_count_observer(nullptr),
+      send_side_delay_observer(nullptr) {
 }
 
 RtpRtcp* RtpRtcp::CreateRtpRtcp(const RtpRtcp::Configuration& configuration) {
@@ -65,6 +66,8 @@ ModuleRtpRtcpImpl::ModuleRtpRtcpImpl(const Configuration& configuration)
                   configuration.outgoing_transport,
                   configuration.audio_messages,
                   configuration.paced_sender,
+                  configuration.packet_router,
+                  configuration.send_time_callback,
                   configuration.send_bitrate_observer,
                   configuration.send_frame_count_observer,
                   configuration.send_side_delay_observer),