Fix for issue 25236

runtime/vm/gc_sweeper.cc

 // Copyright (c) 2011, 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 "vm/gc_sweeper.h"
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/heap.h"
 #include "vm/lockers.h"
@@ skipping 96 matching lines @@
     ASSERT(first_ != NULL);
     ASSERT(old_space_ != NULL);
     ASSERT(last_ != NULL);
     ASSERT(freelist_ != NULL);
     MonitorLocker ml(old_space_->tasks_lock());
     old_space_->set_tasks(old_space_->tasks() + 1);
     ml.Notify();
   }
 
   virtual void Run() {
-    Thread::EnterIsolateAsHelper(task_isolate_);
+    bool result = Thread::EnterIsolateAsHelper(task_isolate_);
+    ASSERT(result);
     GCSweeper sweeper;
 
     HeapPage* page = first_;
     HeapPage* prev_page = NULL;
 
     while (page != NULL) {
       task_isolate_->thread_registry()->CheckSafepoint();
       HeapPage* next_page = page->next();
       ASSERT(page->type() == HeapPage::kData);
       bool page_in_use = sweeper.SweepPage(page, freelist_, false);
@@ skipping 37 matching lines @@
   SweeperTask* task =
       new SweeperTask(isolate,
                       isolate->heap()->old_space(),
                       first, last,
                       freelist);
   ThreadPool* pool = Dart::thread_pool();
   pool->Run(task);
 }
 
 }  // namespace dart