Adds a CancellableTaskFactory and exposes postLoadingTasks to Blink

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 "platform/TraceLocation.h"
+#include "public/platform/Platform.h"
+#include "wtf/InstanceCounter.h"
+
+namespace blink {
+
+void CancellableTaskFactory::cancel()
+{
+    m_weakPtrFactory.revokeAll();
+}
+
+WebThread::Task* CancellableTaskFactory::task()
+{
+    cancel();
+    return new CancellableTask(m_weakPtrFactory.createWeakPtr());
+}
+
+void CancellableTaskFactory::CancellableTask::run()
+{
+    if (m_weakPtr.get()) {
+        Closure* closure = m_weakPtr->m_closure.get();
+        m_weakPtr->m_weakPtrFactory.revokeAll();
+        (*closure)();
+    }
+}
+
+} // namespace blink