Fix performance regression in WebGL to 2D canvas draws.

third_party/WebKit/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 1108 matching lines @@
     if (!isPaintable()) {
         *status = InvalidSourceImageStatus;
         return nullptr;
     }
 
     if (!m_context) {
         *status = NormalSourceImageStatus;
         return createTransparentImage(size());
     }
 
+    sk_sp<SkImage> skImage;
     if (m_context->is3d()) {
-        m_context->paintRenderingResultsToCanvas(BackBuffer);
+        // Because WebGL sources always require making a copy of the back buffer, we
+        // use paintRenderingResultsToCanvas instead of getImage in order to keep a cached
+        // copy of the backing in the canvas's ImageBuffer.
+        renderingContext()->paintRenderingResultsToCanvas(BackBuffer);
+        skImage = hasImageBuffer() ? buffer()->newSkImageSnapshot(hint, reason) : createTransparentImage(size())->imageForCurrentFrame();
+    } else {
+        RefPtr<blink::Image> image = renderingContext()->getImage(hint, reason);
+        skImage = image ? image->imageForCurrentFrame() : createTransparentImage(size())->imageForCurrentFrame();
     }
 
-    sk_sp<SkImage> skImage;
-    RefPtr<blink::Image> image = renderingContext()->getImage(reason);
-
-    if (image)
-        skImage = image->imageForCurrentFrame();
-
     if (skImage) {
         *status = NormalSourceImageStatus;
         return StaticBitmapImage::create(std::move(skImage));
     }
 
     *status = InvalidSourceImageStatus;
     return nullptr;
 }
 
 bool HTMLCanvasElement::wouldTaintOrigin(SecurityOrigin*) const
@@ skipping 101 matching lines @@
 
 bool HTMLCanvasElement::createSurfaceLayer()
 {
     DCHECK(!m_surfaceLayerBridge);
     std::unique_ptr<CanvasSurfaceLayerBridgeClient> bridgeClient = wrapUnique(new CanvasSurfaceLayerBridgeClientImpl());
     m_surfaceLayerBridge = wrapUnique(new CanvasSurfaceLayerBridge(std::move(bridgeClient)));
     return m_surfaceLayerBridge->createSurfaceLayer(this->width(), this->height());
 }
 
 } // namespace blink