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

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
===================================================================
--- runtime/vm/dart_api_impl_test.cc	(revision 1518)
+++ runtime/vm/dart_api_impl_test.cc	(working copy)
@@ -7,6 +7,7 @@
 #include "vm/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_state.h"
+#include "vm/port.h"
 #include "vm/unit_test.h"
 #include "vm/utils.h"
 #include "vm/verifier.h"
@@ -788,6 +789,9 @@
   EXPECT(NULL == Isolate::Current());
 }
 
+static void MyCreatePortCallback(Dart_Isolate dest_isolate,
+                                 Dart_Port port) {
+}
 
 static bool MyPostMessageCallback(Dart_Isolate dest_isolate,
                                   Dart_Port send_port,
@@ -804,8 +808,10 @@
 
 UNIT_TEST_CASE(SetMessageCallbacks) {
   Dart_Isolate dart_isolate = Dart_CreateIsolate(NULL, NULL);
-  Dart_SetMessageCallbacks(&MyPostMessageCallback, &MyClosePortCallback);
+  Dart_SetMessageCallbacks(
+      &MyCreatePortCallback, &MyPostMessageCallback, &MyClosePortCallback);
   Isolate* isolate = reinterpret_cast<Isolate*>(dart_isolate);
+  EXPECT_EQ(&MyCreatePortCallback, isolate->create_port_callback());
   EXPECT_EQ(&MyPostMessageCallback, isolate->post_message_callback());
   EXPECT_EQ(&MyClosePortCallback, isolate->close_port_callback());
   Dart_ShutdownIsolate();
@@ -2123,6 +2129,8 @@
   }
   Dart_ShutdownIsolate();
 }
+
 #endif  // TARGET_ARCH_IA32.
 
+
 }  // namespace dart