Reland "Avoid critsect for protection- and qm setting callbacks in

VideoSender."

The original Cl is uploaded as patch set 1, the fix in ps#2 and I'll rebase in ps#3.

BUG=4534
R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46769004

Cr-Commit-Position: refs/heads/master@{#9000}

webrtc/modules/rtp_rtcp/source/rtp_sender_unittest.cc

@@ -1353,7 +1353,7 @@ TEST_F(RtpSenderVideoTest, SendVideoWithCVO) {
 
   rtp_sender_video_->SendVideo(kRtpVideoGeneric, kVideoFrameKey, kPayload,
                                kTimestamp, 0, packet_, sizeof(packet_), NULL,
-                               NULL, &hdr);
+                               &hdr);
 
   RtpHeaderExtensionMap map;
   map.Register(kRtpExtensionVideoRotation, kVideoRotationExtensionId);