Fix deadlock that can occur while handling service messages at a breakpoint.

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 1115 matching lines @@
  *
  * This function may be used by an embedder at a breakpoint to avoid
  * pausing the vm service.
  *
  * \return true if the vm service requests the program resume
  * execution, false otherwise
  */
 DART_EXPORT bool Dart_HandleServiceMessages();
 
 /**
+ * Does the current isolate have pending service messages?
+ *
+ * \return true if the isolate has pending service messages, false otherwise.
+ */
+DART_EXPORT bool Dart_HasServiceMessages();
+
+/**
  * Processes any incoming messages for the current isolate.
  *
  * This function may only be used when the embedder has not provided
  * an alternate message delivery mechanism with
  * Dart_SetMessageCallbacks. It is provided for convenience.
  *
  * This function waits for incoming messages for the current
  * isolate. As new messages arrive, they are handled using
  * Dart_HandleMessage. The routine exits when all ports to the
  * current isolate are closed.
@@ skipping 1692 matching lines @@
  * NOTE: If multiple callbacks with the same name are registered, only the
  * last callback registered will be remembered.
  */
 DART_EXPORT void Dart_RegisterRootServiceRequestCallback(
     const char* name,
     Dart_ServiceRequestCallback callback,
     void* user_data);
 
 
 #endif  /* INCLUDE_DART_API_H_ */  /* NOLINT */