Fix NativeMessageHandler leak

runtime/vm/native_api_impl.cc

Index: runtime/vm/native_api_impl.cc
diff --git a/runtime/vm/native_api_impl.cc b/runtime/vm/native_api_impl.cc
index 1bc5d4c2305f1d2287cd453a3914ea8fae786e74..dd4350cc6e5f52552221efdb5e6ad8dcdc7f6c02 100644
--- a/runtime/vm/native_api_impl.cc
+++ b/runtime/vm/native_api_impl.cc
@@ -90,6 +90,9 @@ DART_EXPORT Dart_Port Dart_NewNativePort(const char* name,
 
   NativeMessageHandler* nmh = new NativeMessageHandler(name, handler);
   Dart_Port port_id = PortMap::CreatePort(nmh);
+  // Mark that the port is a live port so that PortMap::ClosePort decrements
+  // the live port count when it is closed.
+  PortMap::SetPortState(port_id, PortMap::kLivePort);
   nmh->Run(Dart::thread_pool(), NULL, NULL, 0);
   return port_id;
 }