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

Source/platform/heap/MarkingVisitor.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 MarkingVisitor_h
 #define MarkingVisitor_h
 
 #include "platform/heap/MarkingVisitorImpl.h"
 
 namespace blink {
 
 template <Visitor::MarkingMode Mode>
 class MarkingVisitor final : public Visitor, public MarkingVisitorImpl<MarkingVisitor<Mode>> {
 public:
     using Impl = MarkingVisitorImpl<MarkingVisitor<Mode>>;
     friend class MarkingVisitorImpl<MarkingVisitor<Mode>>;
 
     MarkingVisitor()
         : Visitor(Mode)
     {
     }
 
-    virtual void markHeader(HeapObjectHeader* header, TraceCallback callback) override
+    void markHeader(HeapObjectHeader* header, TraceCallback callback) override
     {
         Impl::markHeader(header, header->payload(), callback);
     }
 
-    virtual void mark(const void* objectPointer, TraceCallback callback) override
+    void mark(const void* objectPointer, TraceCallback callback) override
     {
         Impl::mark(objectPointer, callback);
     }
 
-    virtual void registerDelayedMarkNoTracing(const void* object) override
+    void registerDelayedMarkNoTracing(const void* object) override
     {
         Impl::registerDelayedMarkNoTracing(object);
     }
 
-    virtual void registerWeakMembers(const void* closure, const void* objectPointer, WeakCallback callback) override
+    void registerWeakMembers(const void* closure, const void* objectPointer, WeakCallback callback) override
     {
         Impl::registerWeakMembers(closure, objectPointer, callback);
     }
 
     virtual void registerWeakTable(const void* closure, EphemeronCallback iterationCallback, EphemeronCallback iterationDoneCallback)
     {
         Impl::registerWeakTable(closure, iterationCallback, iterationDoneCallback);
     }
 
 #if ENABLE(ASSERT)
     virtual bool weakTableRegistered(const void* closure)
     {
         return Impl::weakTableRegistered(closure);
     }
 #endif
 
-    virtual bool ensureMarked(const void* objectPointer) override
+    bool ensureMarked(const void* objectPointer) override
     {
         return Impl::ensureMarked(objectPointer);
     }
 
 protected:
-    virtual void registerWeakCellWithCallback(void** cell, WeakCallback callback) override
+    void registerWeakCellWithCallback(void** cell, WeakCallback callback) override
     {
         Impl::registerWeakCellWithCallback(cell, callback);
     }
 
     inline bool shouldMarkObject(const void* objectPointer)
     {
         if (Mode != ThreadLocalMarking)
             return true;
 
         BasePage* page = pageFromObject(objectPointer);
         ASSERT(!page->orphaned());
         // When doing a thread local GC, the marker checks if
         // the object resides in another thread's heap. If it
         // does, the object should not be marked & traced.
         return page->terminating();
     }
 };
 
 } // namespace blink
 
 #endif