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

Source/platform/scheduler/CancellableTaskFactory.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/scheduler/CancellableTaskFactory.h"
 
-#include "public/platform/Platform.h"
-#include "wtf/InstanceCounter.h"
-
 namespace blink {
 
 void CancellableTaskFactory::cancel()
 {
-    m_weakPtrFactory.revokeAll();
+    ASSERT(m_thread == currentThread());
+
+    if (m_task) {
+        m_task->cancel();
+        m_task = nullptr;
+    }
 }
 
 WebThread::Task* CancellableTaskFactory::task()
 {
+    ASSERT(m_thread == currentThread());
+
     cancel();
-    return new CancellableTask(m_weakPtrFactory.createWeakPtr());
+    m_task = new CancellableTask(this);
+    return m_task;
 }
 
 void CancellableTaskFactory::CancellableTask::run()
 {
-    if (m_weakPtr.get()) {
-        Closure* closure = m_weakPtr->m_closure.get();
-        m_weakPtr->m_weakPtrFactory.revokeAll();
-        (*closure)();
+    if (m_factory) {
+        ASSERT(m_factory->m_thread == currentThread());
+        m_factory->m_task = nullptr;
+        (*m_factory->m_closure)();
+        m_factory = nullptr;
     }
 }
 
 } // namespace blink