Hide Isolate pointer from embedder

runtime/bin/dbg_connection.cc

Index: runtime/bin/dbg_connection.cc
diff --git a/runtime/bin/dbg_connection.cc b/runtime/bin/dbg_connection.cc
index 2cc4cd83ffa761e4bc780f45c94c038b0980486a..1a53c598a4c65eb89b030e4ce250ed805e9998eb 100644
--- a/runtime/bin/dbg_connection.cc
+++ b/runtime/bin/dbg_connection.cc
@@ -455,7 +455,8 @@ void DebuggerConnectionHandler::HandleInterruptCmd(DbgMessage* in_msg) {
   MessageParser msg_parser(in_msg->buffer(), in_msg->buffer_len());
   int msg_id = msg_parser.MessageId();
   Dart_IsolateId isolate_id = msg_parser.GetInt64Param("isolateId");
-  if (isolate_id == ILLEGAL_ISOLATE_ID || Dart_GetIsolate(isolate_id) == NULL) {
+  if (isolate_id == ILLEGAL_ISOLATE_ID ||
+      Dart_GetIsolate(isolate_id) == ILLEGAL_ISOLATE) {
     in_msg->SendErrorReply(msg_id, "Invalid isolate specified");
     return;
   }