Fix virtual/override/final usage in Source/platform/.

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/AddressSanitizer.h"
@@ skipping 39 matching lines @@
     // unpoisoning first.
     void setUnpoisonBeforeUpdate() { m_unpoisonBeforeUpdate = true; }
 #endif
 
 private:
     class CancellableTask : public WebThread::Task {
         WTF_MAKE_NONCOPYABLE(CancellableTask);
 
     public:
         explicit CancellableTask(WeakPtr<CancellableTaskFactory> weakPtr)
-            : m_weakPtr(weakPtr) { }
+            : m_weakPtr(weakPtr) {}
 
-        virtual ~CancellableTask() { }
+        ~CancellableTask() override {}
 
         void run() override;
 
     private:
         WeakPtr<CancellableTaskFactory> m_weakPtr;
     };
 
     OwnPtr<Closure> m_closure;
 #if defined(ADDRESS_SANITIZER)
     bool m_unpoisonBeforeUpdate;
 #endif
     WeakPtrFactory<CancellableTaskFactory> m_weakPtrFactory;
 };
 
 } // namespace blink
 
 #endif // CancellableTaskFactory_h