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

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
===================================================================
--- runtime/vm/dart_api_impl.cc	(revision 1518)
+++ runtime/vm/dart_api_impl.cc	(working copy)
@@ -275,12 +275,15 @@
 
 
 DART_EXPORT void Dart_SetMessageCallbacks(
+    Dart_CreatePortCallback create_port_callback,
     Dart_PostMessageCallback post_message_callback,
     Dart_ClosePortCallback close_port_callback) {
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate != NULL);
+  ASSERT(create_port_callback != NULL);
   ASSERT(post_message_callback != NULL);
   ASSERT(close_port_callback != NULL);
+  isolate->set_create_port_callback(create_port_callback);
   isolate->set_post_message_callback(post_message_callback);
   isolate->set_close_port_callback(close_port_callback);
 }
@@ -1932,6 +1935,18 @@
 }
 
 
+DART_EXPORT Dart_Port Dart_CreatePort() {
+  return PortMap::CreatePort();
+}
+
+
+DART_EXPORT bool Dart_IsolateHasActivePorts() {
+  Isolate* isolate = Isolate::Current();
+  ASSERT(isolate);
+  return isolate->active_ports() > 0;
+}
+
+
 static uint8_t* allocator(uint8_t* ptr, intptr_t old_size, intptr_t new_size) {
   void* new_ptr = realloc(reinterpret_cast<void*>(ptr), new_size);
   return reinterpret_cast<uint8_t*>(new_ptr);