Wire up transport sequence number / send time callbacks to webrtc via libjingle.

talk/media/webrtc/webrtcvoiceengine.cc

Index: talk/media/webrtc/webrtcvoiceengine.cc
diff --git a/talk/media/webrtc/webrtcvoiceengine.cc b/talk/media/webrtc/webrtcvoiceengine.cc
index a3ea0f9a74d2683e24f7a9adb660f51d0d689f84..caaf87ea07c363a1aa80d102017f7e2000dd615d 100644
--- a/talk/media/webrtc/webrtcvoiceengine.cc
+++ b/talk/media/webrtc/webrtcvoiceengine.cc
@@ -52,6 +52,7 @@
 #include "webrtc/base/stringutils.h"
 #include "webrtc/common.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
+#include "webrtc/system_wrappers/interface/field_trial.h"
 
 namespace cricket {
 namespace {
@@ -431,6 +432,11 @@ void WebRtcVoiceEngine::Construct() {
   rtp_header_extensions_.push_back(
       RtpHeaderExtension(kRtpAbsoluteSenderTimeHeaderExtension,
                          kRtpAbsoluteSenderTimeHeaderExtensionDefaultId));
+  if (webrtc::field_trial::FindFullName("WebRTC-SendSideBwe") == "Enabled") {
+    rtp_header_extensions_.push_back(RtpHeaderExtension(
+        kRtpTransportSequenceNumberHeaderExtension,
+        kRtpTransportSequenceNumberHeaderExtensionDefaultId));
+  }
   options_ = GetDefaultEngineOptions();
 }