Determine if OffscreenCanvas is paintable in different rendering contexts

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.h

 /*
  * Copyright (C) 2006, 2007, 2009, 2010, 2011, 2012 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 206 matching lines @@
     LostContextMode m_contextLostMode;
     bool m_contextRestorable;
     unsigned m_tryRestoreContextAttemptCount;
     Timer<CanvasRenderingContext2D> m_dispatchContextLostEventTimer;
     Timer<CanvasRenderingContext2D> m_dispatchContextRestoredEventTimer;
     Timer<CanvasRenderingContext2D> m_tryRestoreContextEventTimer;
 
     HashMap<String, Font> m_fontsResolvedUsingCurrentStyle;
     bool m_pruneLocalFontCacheScheduled;
     ListHashSet<String> m_fontLRUList;
+
+    bool isPaintable() const final
+    {
+        NOTREACHED();
+        return false;
+    }
 };
 
 DEFINE_TYPE_CASTS(CanvasRenderingContext2D, CanvasRenderingContext, context,
     context->is2d() && context->canvas(), context.is2d() && context.canvas());
 
 } // namespace blink
 
 #endif // CanvasRenderingContext2D_h