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

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 "vm/class_finalizer.h"
@@ skipping 1529 matching lines @@
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE_SCOPE(isolate);
   CHECK_CALLBACK_STATE(isolate);
 
   ASSERT(isolate->GetAndClearResumeRequest() == false);
   isolate->message_handler()->HandleOOBMessages();
   return isolate->GetAndClearResumeRequest();
 }
 
 
+DART_EXPORT bool Dart_HasServiceMessages() {
+  Isolate* isolate = Isolate::Current();
+  ASSERT(isolate);
+  return isolate->message_handler()->HasOOBMessages();
+}
+
+
 DART_EXPORT bool Dart_HasLivePorts() {
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate);
   return isolate->message_handler()->HasLivePorts();
 }
 
 
 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);
@@ skipping 3846 matching lines @@
 
 
 DART_EXPORT void Dart_RegisterRootServiceRequestCallback(
     const char* name,
     Dart_ServiceRequestCallback callback,
     void* user_data) {
   Service::RegisterRootEmbedderCallback(name, callback, user_data);
 }
 
 }  // namespace dart