Bug 1626278: Move sigslot stuff to STS, and ensure we disconnect before releasing our ref to the MediaTransportHandler. r=mjf

This patch fixes an intermittent crash in pre-existing mochitests/wpt.

Differential Revision: https://phabricator.services.mozilla.com/D90626

dom/media/webrtc/jsapi/TransceiverImpl.cpp

@@ -89,10 +89,16 @@ TransceiverImpl::TransceiverImpl(
 
   mTransmitPipeline->SetTrack(mSendTrack);
 
-  mTransportHandler->SignalStateChange.connect(
-      this, &TransceiverImpl::UpdateDtlsTransportState);
-  mTransportHandler->SignalRtcpStateChange.connect(
-      this, &TransceiverImpl::UpdateDtlsTransportState);
+  auto self = nsMainThreadPtrHandle<TransceiverImpl>(
+      new nsMainThreadPtrHolder<TransceiverImpl>(
+          "TransceiverImpl::TransceiverImpl::self", this, false));
+  mStsThread->Dispatch(
+      NS_NewRunnableFunction("TransceiverImpl::TransceiverImpl", [self] {
+        self->mTransportHandler->SignalStateChange.connect(
+            self.get(), &TransceiverImpl::UpdateDtlsTransportState);
+        self->mTransportHandler->SignalRtcpStateChange.connect(
+            self.get(), &TransceiverImpl::UpdateDtlsTransportState);
+      }));
 }
 
 TransceiverImpl::~TransceiverImpl() = default;
@@ -168,7 +174,13 @@ void TransceiverImpl::Shutdown_m() {
   }
   Stop();
   mTransmitPipeline = nullptr;
-  mTransportHandler = nullptr;
+  auto self = nsMainThreadPtrHandle<TransceiverImpl>(
+      new nsMainThreadPtrHolder<TransceiverImpl>(
+          "TransceiverImpl::Shutdown_m::self", this, false));
+  mStsThread->Dispatch(NS_NewRunnableFunction(__func__, [self] {
+    self->disconnect_all();
+    self->mTransportHandler = nullptr;
+  }));
 }
 
 nsresult TransceiverImpl::UpdateSendTrack(dom::MediaStreamTrack* aSendTrack) {