Fix virtual/override/final usage in Source/core/html/.

Source/core/html/canvas/CanvasRenderingContext.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 29 matching lines @@
 
 class CanvasImageSource;
 class HTMLCanvasElement;
 class ImageData;
 
 class CORE_EXPORT CanvasRenderingContext : public NoBaseWillBeGarbageCollectedFinalized<CanvasRenderingContext>, public ActiveDOMObject, public ScriptWrappable {
     WTF_MAKE_NONCOPYABLE(CanvasRenderingContext);
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED(CanvasRenderingContext);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(CanvasRenderingContext);
 public:
-    virtual ~CanvasRenderingContext() { }
+    ~CanvasRenderingContext() override { }
 
     // A Canvas can either be "2D" or "webgl" but never both. If you request a 2D canvas and the existing
     // context is already 2D, just return that. If the existing context is WebGL, then destroy it
     // before creating a new 2D context. Vice versa when requesting a WebGL canvas. Requesting a
     // context with any other type string will destroy any existing context.
     enum ContextType {
         // Do not change assigned numbers of existing items: add new features to the end of the list.
         Context2d = 0,
         ContextExperimentalWebgl = 2,
         ContextWebgl = 3,
@@ skipping 34 matching lines @@
     virtual int externallyAllocatedBytesPerPixel() { ASSERT_NOT_REACHED(); return 0; }
 
     bool wouldTaintOrigin(CanvasImageSource*);
     void didMoveToNewDocument(Document*);
 
 protected:
     CanvasRenderingContext(HTMLCanvasElement*);
     DECLARE_VIRTUAL_TRACE();
 
     // ActiveDOMObject notifications
-    bool hasPendingActivity() const override final;
+    bool hasPendingActivity() const final;
     void stop() override = 0;
 
 private:
     RawPtrWillBeMember<HTMLCanvasElement> m_canvas;
     HashSet<String> m_cleanURLs;
     HashSet<String> m_dirtyURLs;
 };
 
 } // namespace blink
 
 #endif