Add Dart_GetMessageNotifyCallback for querying the current message notify callback

runtime/include/dart_api.h

 /*
  * Copyright (c) 2012, 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.
  */
 
 #ifndef INCLUDE_DART_API_H_
 #define INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
@@ skipping 1060 matching lines @@
  * Most embedders will only call this function once, before isolate
  * execution begins. If this function is called after isolate
  * execution begins, the embedder is responsible for threading issues.
  */
 DART_EXPORT void Dart_SetMessageNotifyCallback(
     Dart_MessageNotifyCallback message_notify_callback);
 /* TODO(turnidge): Consider moving this to isolate creation so that it
  * is impossible to mess up. */
 
 /**
+ * Query the current message notify callback for the isolate.
+ *
+ * \return The current message notify callback for the isolate.
+ */
+DART_EXPORT Dart_MessageNotifyCallback Dart_GetMessageNotifyCallback();
+
+/**
  * The VM's default message handler supports pausing an isolate before it
  * processes the first message and right after the it processes the isolate's
  * final message. This can be controlled for all isolates by two VM flags:
  *
  *   `--pause-isolates-on-start`
  *   `--pause-isolates-on-exit`
  *
  * Additionally, Dart_SetShouldPauseOnStart and Dart_SetShouldPauseOnExit can be
  * used to control this behaviour on a per-isolate basis.
  *
@@ skipping 1852 matching lines @@
     intptr_t* vm_isolate_snapshot_size,
     uint8_t** isolate_snapshot_buffer,
     intptr_t* isolate_snapshot_size,
     uint8_t** instructions_snapshot_buffer,
     intptr_t* instructions_snapshot_size);
 
 
 DART_EXPORT bool Dart_IsRunningPrecompiledCode();
 
 #endif  /* INCLUDE_DART_API_H_ */  /* NOLINT */