Disable GPU acceleration on 2D canvas when readbacks are needed

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 1272 matching lines @@
   sk_sp<SkImage> skImage;
   if (m_context->is3d()) {
     // 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 {
+    if (ExpensiveCanvasHeuristicParameters::
+            DisableAccelerationToAvoidReadbacks &&
+        !RuntimeEnabledFeatures::canvas2dFixedRenderingModeEnabled() &&
+        hint == PreferNoAcceleration && m_context->isAccelerated() &&
+        hasImageBuffer())
+      buffer()->disableAcceleration();
     RefPtr<blink::Image> image = renderingContext()->getImage(hint, reason);
     skImage = image ? image->imageForCurrentFrame()
                     : createTransparentImage(size())->imageForCurrentFrame();
   }
 
   if (skImage) {
     *status = NormalSourceImageStatus;
     return StaticBitmapImage::create(std::move(skImage));
   }
 
@@ skipping 116 matching lines @@
   mojom::blink::OffscreenCanvasSurfacePtr service;
   Platform::current()->interfaceProvider()->getInterface(
       mojo::GetProxy(&service));
   m_surfaceLayerBridge =
       wrapUnique(new CanvasSurfaceLayerBridge(std::move(service)));
   return m_surfaceLayerBridge->createSurfaceLayer(this->width(),
                                                   this->height());
 }
 
 }  // namespace blink