Avoid critsect for protection- and qm setting callbacks in VideoSender.

This CL avoids changing the mentioned callbacks during a call, to avoid
a potential deadlock when acquiring _sendCritSect and calling
_mediaOpt.SetTargetRates.

Moving the critsect revealed a race for the FEC parameters in RtpVideoSender, so the CL grew a bit to avoid this. I also cleaned up some code here at the same time, but tried to keep it at a minimum since this CL had already increased a lot in size.

BUG=769
R=pbos@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/42939004

Cr-Commit-Position: refs/heads/master@{#8899}

webrtc/modules/video_coding/main/source/media_optimization.cc

@@ -246,7 +246,7 @@ uint32_t MediaOptimization::SetTargetRates(
 
   // Update protection settings, when applicable.
   float sent_video_rate_kbps = 0.0f;
-  if (selected_method) {
+  if (loss_prot_logic_->SelectedType() != kNone) {
     // Update protection method with content metrics.
     selected_method->UpdateContentMetrics(content_->ShortTermAvgData());