Fix for issue 21398 (only send "literal like" objects across isolates spawned using spawnURI

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/class_finalizer.h"
@@ skipping 1558 matching lines @@
   void* new_ptr = realloc(reinterpret_cast<void*>(ptr), new_size);
   return reinterpret_cast<uint8_t*>(new_ptr);
 }
 
 
 DART_EXPORT bool Dart_Post(Dart_Port port_id, Dart_Handle handle) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   const Object& object = Object::Handle(isolate, Api::UnwrapHandle(handle));
   uint8_t* data = NULL;
-  MessageWriter writer(&data, &allocator);
+  MessageWriter writer(&data, &allocator, false);
   writer.WriteMessage(object);
   intptr_t len = writer.BytesWritten();
   return PortMap::PostMessage(new Message(
       port_id, data, len, Message::kNormalPriority));
 }
 
 
 DART_EXPORT Dart_Handle Dart_NewSendPort(Dart_Port port_id) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
@@ skipping 3834 matching lines @@
 
 
 DART_EXPORT void Dart_RegisterRootServiceRequestCallback(
     const char* name,
     Dart_ServiceRequestCallback callback,
     void* user_data) {
   Service::RegisterRootEmbedderCallback(name, callback, user_data);
 }
 
 }  // namespace dart