Add option to print peer connection factory Java stack traces.

R=wzh@webrtc.org

Review URL: https://codereview.webrtc.org/1395693002 .

Cr-Commit-Position: refs/heads/master@{#10204}
diff --git a/talk/app/webrtc/java/jni/classreferenceholder.cc b/talk/app/webrtc/java/jni/classreferenceholder.cc
index 25b72da..d99aa1a 100644
--- a/talk/app/webrtc/java/jni/classreferenceholder.cc
+++ b/talk/app/webrtc/java/jni/classreferenceholder.cc
@@ -99,6 +99,7 @@
   LoadClass(jni, "org/webrtc/MediaSource$State");
   LoadClass(jni, "org/webrtc/MediaStream");
   LoadClass(jni, "org/webrtc/MediaStreamTrack$State");
+  LoadClass(jni, "org/webrtc/PeerConnectionFactory");
   LoadClass(jni, "org/webrtc/PeerConnection$BundlePolicy");
   LoadClass(jni, "org/webrtc/PeerConnection$ContinualGatheringPolicy");
   LoadClass(jni, "org/webrtc/PeerConnection$RtcpMuxPolicy");