Refactor TimeBase to post tasks. Workers to use real Idle tasks.

Source/core/workers/WorkerGlobalScope.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009, 2011 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 165 matching lines @@
 
 void WorkerGlobalScope::close()
 {
     if (m_closing)
         return;
 
     // Let current script run to completion but prevent future script evaluations.
     // After m_closing is set, all the tasks in the queue continue to be fetched but only
     // tasks with isCleanupTask()==true will be executed.
     m_closing = true;
+    m_thread->preShutdown();
     postTask(FROM_HERE, CloseWorkerGlobalScopeTask::create());
 }
 
 WorkerConsole* WorkerGlobalScope::console()
 {
     if (!m_console)
         m_console = WorkerConsole::create(this);
     return m_console.get();
 }
 
@@ skipping 200 matching lines @@
     visitor->trace(m_timers);
     visitor->trace(m_messageStorage);
     visitor->trace(m_pendingMessages);
     HeapSupplementable<WorkerGlobalScope>::trace(visitor);
 #endif
     ExecutionContext::trace(visitor);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink