Revert of Remove SendPacer from ViEEncoder

webrtc/video/video_send_stream.cc

Index: webrtc/video/video_send_stream.cc
diff --git a/webrtc/video/video_send_stream.cc b/webrtc/video/video_send_stream.cc
index e87f56f383edbb3bddb2c4bb4e5a3860fdeff2a5..9e38384381f8d76ac15ef4b0d3b8e59457f82ae3 100644
--- a/webrtc/video/video_send_stream.cc
+++ b/webrtc/video/video_send_stream.cc
@@ -376,7 +376,9 @@
                    config_.rtp.ssrcs,
                    module_process_thread_,
                    &stats_proxy_,
-                   &overuse_detector_),
+                   config.pre_encode_callback,
+                   &overuse_detector_,
+                   congestion_controller_->pacer()),
       video_sender_(vie_encoder_.video_sender()),
       bandwidth_observer_(congestion_controller_->GetBitrateController()
                               ->CreateRtcpBandwidthObserver()),
@@ -576,14 +578,8 @@
     }
 
     VideoFrame frame;
-    if (input_.GetVideoFrame(&frame)) {
-      // TODO(perkj): |pre_encode_callback| is only used by tests. Tests should
-      // register as a sink to the VideoSource instead.
-      if (config_.pre_encode_callback) {
-        config_.pre_encode_callback->OnFrame(frame);
-      }
+    if (input_.GetVideoFrame(&frame))
       vie_encoder_.EncodeVideoFrame(frame);
-    }
   }
   vie_encoder_.DeRegisterExternalEncoder(config_.encoder_settings.payload_type);
 }