Adds a CancellableTaskFactory and exposes postLoadingTasks to Blink

Source/platform/scheduler/CancellableTaskFactory.h

Index: Source/platform/scheduler/CancellableTaskFactory.h
diff --git a/Source/platform/scheduler/CancellableTaskFactory.h b/Source/platform/scheduler/CancellableTaskFactory.h
new file mode 100644
index 0000000000000000000000000000000000000000..58a66c0dd51a93aa32edf286b2fe4003417394ec
--- /dev/null
+++ b/Source/platform/scheduler/CancellableTaskFactory.h
@@ -0,0 +1,57 @@
+// 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.
+
+#ifndef CancellableTaskFactory_h
+#define CancellableTaskFactory_h
+
+#include "platform/PlatformExport.h"
+#include "public/platform/WebScheduler.h"
+#include "wtf/Functional.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/RefCounted.h"
+#include "wtf/WeakPtr.h"
+
+namespace blink {
+class TraceLocation;
+
+class PLATFORM_EXPORT CancellableTaskFactory {
+    WTF_MAKE_NONCOPYABLE(CancellableTaskFactory);
+public:
+    explicit CancellableTaskFactory(PassOwnPtr<Closure> closure) : m_closure(closure), m_weakPtrFactory(this) { }
+
+    bool isPending() const
+    {
+        return m_weakPtrFactory.hasWeakPtrs();
+    }
+
+    void cancel();
+
+    // Returns a task that can be disabled by calling cancel().  The user takes
+    // ownership of the task.  Creating a new task cancels any previous ones.
+    WebThread::Task* task();
+
+private:
+    class CancellableTask : public WebThread::Task {
+        WTF_MAKE_NONCOPYABLE(CancellableTask);
+    public:
+        explicit CancellableTask(WeakPtr<CancellableTaskFactory> weakPtr) : m_weakPtr(weakPtr) { }
+        virtual ~CancellableTask() { }
+
+        void run() override;
+
+    private:
+        WeakPtr<CancellableTaskFactory> m_weakPtr;
+    };
+
+    OwnPtr<Closure> m_closure;
+    WeakPtrFactory<CancellableTaskFactory> m_weakPtrFactory;
+
+    friend class CancellableTask;
+};
+
+} // namespace blink
+
+#endif // CancellableTaskFactory_h