Bug 1290049 - only process ice connection state change if new state differs from old state. r=bwc

MozReview-Commit-ID: KAM1XVIn4Qw

--HG--
extra : rebase_source : 18244caa318b8bccd969cd50069265b467477f26

media/webrtc/signaling/src/peerconnection/PeerConnectionImpl.cpp

@@ -3417,6 +3417,11 @@ void PeerConnectionImpl::IceConnectionStateChange(
   CSFLogDebug(logTag, "%s", __FUNCTION__);
 
   auto domState = toDomIceConnectionState(state);
+  if (domState == mIceConnectionState) {
+    // no work to be done since the states are the same.
+    // this can happen during ICE rollback situations.
+    return;
+  }
 
 #if !defined(MOZILLA_EXTERNAL_LINKAGE)
   if (!isDone(mIceConnectionState) && isDone(domState)) {