[chaotic-good] Don't add new streams after transport closed (#37887)

Prior to this change events could conspire such that newly read streams got added after the AbortWithError() code ran, and so those calls would be orphaned in the transport forever - continuing to hold a ref.

Closes #37887

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37887 from ctiller:flake-fightas-20 2648d7f37f
PiperOrigin-RevId: 684609806

src/core/ext/transport/chaotic_good/server_transport.cc

@@ -397,6 +397,7 @@ void ChaoticGoodServerTransport::AbortWithError() {
   // Close all the available pipes.
   outgoing_frames_.MarkClosed();
   ReleasableMutexLock lock(&mu_);
+  aborted_with_error_ = true;
   StreamMap stream_map = std::move(stream_map_);
   stream_map_.clear();
   state_tracker_.SetState(GRPC_CHANNEL_SHUTDOWN,
@@ -439,6 +440,9 @@ absl::Status ChaoticGoodServerTransport::NewStream(
   GRPC_TRACE_LOG(chaotic_good, INFO)
       << "CHAOTIC_GOOD " << this << " NewStream " << stream_id;
   MutexLock lock(&mu_);
+  if (aborted_with_error_) {
+    return absl::UnavailableError("Transport closed");
+  }
   auto it = stream_map_.find(stream_id);
   if (it != stream_map_.end()) {
     return absl::InternalError("Stream already exists");

src/core/ext/transport/chaotic_good/server_transport.h

@@ -143,6 +143,7 @@ class ChaoticGoodServerTransport final : public ServerTransport {
   Mutex mu_;
   // Map of stream incoming server frames, key is stream_id.
   StreamMap stream_map_ ABSL_GUARDED_BY(mu_);
+  bool aborted_with_error_ ABSL_GUARDED_BY(mu_) = false;
   uint32_t last_seen_new_stream_id_ = 0;
   RefCountedPtr<Party> party_;
   ConnectivityStateTracker state_tracker_ ABSL_GUARDED_BY(mu_){