Never call GraphicsLayer::paint when fetching painted output from cc.

third_party/WebKit/Source/platform/graphics/ContentLayerDelegate.cpp

 /*
  * Copyright (C) 2012 Google 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 75 matching lines @@
     // to compare assuming the full cost of recording, not the cost of re-using cached content.
     if (paintingControl != WebContentLayerClient::PaintDefaultBehavior
         && paintingControl != WebContentLayerClient::SubsequenceCachingDisabled)
         paintController.invalidateAll();
 
     GraphicsContext::DisabledMode disabledMode = GraphicsContext::NothingDisabled;
     if (paintingControl == WebContentLayerClient::DisplayListPaintingDisabled
         || paintingControl == WebContentLayerClient::DisplayListConstructionDisabled)
         disabledMode = GraphicsContext::FullyDisabled;
 
-    m_graphicsLayer->paint(nullptr, disabledMode);
+    // Anything other than PaintDefaultBehavior is for testing. In non-testing scenarios,
+    // it is an error to call GraphicsLayer::paint. Actual painting occurs in FrameView::synchronizedPaint;
+    // this method merely copies the painted output to the WebDisplayItemList.
+    if (paintingControl != PaintDefaultBehavior)
+        m_graphicsLayer->paint(nullptr, disabledMode);
+
     paintArtifactToWebDisplayItemList(webDisplayItemList, m_graphicsLayer, paintController.paintArtifact(), paintableRegion());
+
     paintController.setDisplayItemConstructionIsDisabled(false);
     paintController.setSubsequenceCachingIsDisabled(false);
 }
 
 size_t ContentLayerDelegate::approximateUnsharedMemoryUsage() const
 {
     return m_graphicsLayer->paintController().approximateUnsharedMemoryUsage();
 }
 
 } // namespace blink