Add a mid-sized integration test for the Dart Embedding Api which

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
===================================================================
--- runtime/vm/isolate.cc	(revision 1518)
+++ runtime/vm/isolate.cc	(working copy)
@@ -34,6 +34,7 @@
 Isolate::Isolate()
     : store_buffer_(),
       message_queue_(NULL),
+      create_port_callback_(NULL),
       post_message_callback_(NULL),
       close_port_callback_(NULL),
       active_ports_(0),
@@ -75,6 +76,12 @@
 }
 
 
+static void StandardCreatePortCallback(Dart_Isolate dart_isolate,
+                                       Dart_Port port) {
+  // Do nothing.
+}
+
+
 static bool StandardPostMessageCallback(Dart_Isolate dart_isolate,
                                         Dart_Port dest_port,
                                         Dart_Port reply_port,
@@ -112,6 +119,7 @@
   MessageQueue* queue = new MessageQueue();
   ASSERT(queue != NULL);
   result->set_message_queue(queue);
+  result->set_create_port_callback(&StandardCreatePortCallback);
   result->set_post_message_callback(&StandardPostMessageCallback);
   result->set_close_port_callback(&StandardClosePortCallback);