Wire up target_media_bitrate in VideoSendStream.

Also wires up target_enc_bitrate in WebRtcVideoEngine2.

BUG=1667,1788
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/42479004

Cr-Commit-Position: refs/heads/master@{#8515}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8515 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/utility/source/video_coder.cc

@@ -14,7 +14,8 @@
 #include "webrtc/modules/video_coding/main/source/encoded_frame.h"
 
 namespace webrtc {
-VideoCoder::VideoCoder() : _vcm(VideoCodingModule::Create()), _decodedVideo(0) {
+VideoCoder::VideoCoder()
+    : _vcm(VideoCodingModule::Create(nullptr)), _decodedVideo(0) {
     _vcm->InitializeSender();
     _vcm->InitializeReceiver();