Fix the definition of kIllegalPort in dart_api.h.

samples/sample_extension/sample_extension.cc

Index: samples/sample_extension/sample_extension.cc
diff --git a/samples/sample_extension/sample_extension.cc b/samples/sample_extension/sample_extension.cc
index 2243c38d88292e6314124f9c89b65c26f90ea8ac..6c9ff2865d775aa1d1c61472aa8ee259d58b4906 100644
--- a/samples/sample_extension/sample_extension.cc
+++ b/samples/sample_extension/sample_extension.cc
@@ -96,7 +96,7 @@ void randomArrayServicePort(Dart_NativeArguments arguments) {
   Dart_SetReturnValue(arguments, Dart_Null());
   Dart_Port service_port =
       Dart_NewNativePort("RandomArrayService", wrappedRandomArray, true);
-  if (service_port != kIllegalPort) {
+  if (service_port != ILLEGAL_PORT) {
     Dart_Handle send_port = HandleError(Dart_NewSendPort(service_port));
     Dart_SetReturnValue(arguments, send_port);
   }