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

Source/platform/scheduler/CancellableTaskFactory.h

 // 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;
 
+// NOTE CancellableTaskFactory is NOT threadsafe.
 class PLATFORM_EXPORT CancellableTaskFactory {
     WTF_MAKE_NONCOPYABLE(CancellableTaskFactory);
 
 public:
     explicit CancellableTaskFactory(PassOwnPtr<Closure> closure)
         : m_closure(closure)
-        , m_weakPtrFactory(this)
+        , m_task(nullptr)
+#if ENABLE(ASSERT)
+        , m_thread(currentThread())
+#endif
     {
     }
 
+    ~CancellableTaskFactory()
+    {
+        cancel();
+    }
+
     bool isPending() const
     {
-        return m_weakPtrFactory.hasWeakPtrs();
+        return m_task;
     }
 
     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);
+        WTF_MAKE_FAST_ALLOCATED;
 
     public:
-        explicit CancellableTask(WeakPtr<CancellableTaskFactory> weakPtr)
-            : m_weakPtr(weakPtr) { }
+        explicit CancellableTask(CancellableTaskFactory* factory)
+            : m_factory(factory)
+        {
+        }
 
         virtual ~CancellableTask() { }
 
         void run() override;
 
+        void cancel()
+        {
+            m_factory = nullptr;
+        }
+
     private:
-        WeakPtr<CancellableTaskFactory> m_weakPtr;
+        CancellableTaskFactory* m_factory; // NOT OWNED
     };
 
     OwnPtr<Closure> m_closure;
-    WeakPtrFactory<CancellableTaskFactory> m_weakPtrFactory;
+    CancellableTask* m_task; // NOT OWNED
+
+#if ENABLE(ASSERT)
+    ThreadIdentifier m_thread;
+#endif
 };
 
 } // namespace blink
 
 #endif // CancellableTaskFactory_h