Add Dart_GetMessageNotifyCallback for querying the current message notify callback

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 "lib/stacktrace.h"
@@ skipping 1559 matching lines @@
 // --- Messages and Ports ---
 
 DART_EXPORT void Dart_SetMessageNotifyCallback(
     Dart_MessageNotifyCallback message_notify_callback) {
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE(isolate);
   isolate->set_message_notify_callback(message_notify_callback);
 }
 
 
+DART_EXPORT Dart_MessageNotifyCallback Dart_GetMessageNotifyCallback() {
+  Isolate* isolate = Isolate::Current();
+  CHECK_ISOLATE(isolate);
+  return isolate->message_notify_callback();
+}
+
+
 struct RunLoopData {
   Monitor* monitor;
   bool done;
 };
 
 
 static void RunLoopDone(uword param) {
   RunLoopData* data = reinterpret_cast<RunLoopData*>(param);
   ASSERT(data->monitor != NULL);
   MonitorLocker ml(data->monitor);
@@ skipping 4514 matching lines @@
   return Api::Success();
 }
 #endif  // DART_PRECOMPILER
 
 
 DART_EXPORT bool Dart_IsRunningPrecompiledCode() {
   return Dart::IsRunningPrecompiledCode();
 }
 
 }  // namespace dart