Adjust DrawingBuffer's visibility tracking behavior with lost context

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * 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 866 matching lines @@
 }
 
 void WebGLRenderingContextBase::markLayerComposited()
 {
     if (!isContextLost())
         drawingBuffer()->markLayerComposited();
 }
 
 void WebGLRenderingContextBase::setIsHidden(bool hidden)
 {
-    if (!isContextLost())
+    if (drawingBuffer())
         drawingBuffer()->setIsHidden(hidden);
 }
 
 void WebGLRenderingContextBase::paintRenderingResultsToCanvas()
 {
     if (isContextLost()) {
         canvas()->clearPresentationCopy();
         return;
     }
 
@@ skipping 4876 matching lines @@
     return m_sharedWebGraphicsContext3D ? m_sharedWebGraphicsContext3D->drawingBuffer() : 0;
 }
 #else
 DrawingBuffer* WebGLRenderingContextBase::drawingBuffer() const
 {
     return m_drawingBuffer.get();
 }
 #endif
 
 } // namespace blink