canvas: fix bugs on HTMLCanvasElement::copiedImage()

Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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.
@@ skipping 719 matching lines @@
     m_didFailToCreateImageBuffer = !m_imageBuffer;
 }
 
 PassRefPtr<Image> HTMLCanvasElement::copiedImage(SourceDrawingBuffer sourceBuffer) const
 {
     if (!isPaintable())
         return nullptr;
     if (!m_context)
         return createTransparentImage(size());
 
-    if (!m_copiedImage && buffer()) {
-        if (m_context && m_context->is3d())
-            m_context->paintRenderingResultsToCanvas(sourceBuffer);
+    bool needToUpdate = !m_copiedImage;
+    // The concept of SourceDrawingBuffer is valid on only WebGL.
+    if (m_context->is3d())
+        needToUpdate |= m_context->paintRenderingResultsToCanvas(sourceBuffer);
+    if (needToUpdate && buffer()) {
         m_copiedImage = buffer()->copyImage(CopyBackingStore, Unscaled);
         updateExternallyAllocatedMemory();
     }
     return m_copiedImage;
 }
 
 void HTMLCanvasElement::discardImageBuffer()
 {
     m_contextStateSaver.clear(); // uses context owned by m_imageBuffer
     m_imageBuffer.clear();
@@ skipping 79 matching lines @@
 {
     return !originClean();
 }
 
 FloatSize HTMLCanvasElement::sourceSize() const
 {
     return FloatSize(width(), height());
 }
 
 }