Cancel GPU acceleration for 2D canvas when drawing very large images

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/offscreencanvas/OffscreenCanvas.h"
 
 #include "core/dom/ExceptionCode.h"
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
@@ skipping 138 matching lines @@
     return m_originClean && !m_disableReadingFromCanvas;
 }
 
 bool OffscreenCanvas::isPaintable() const
 {
     if (!m_context)
         return ImageBuffer::canCreateImageBuffer(m_size);
     return m_context->isPaintable();
 }
 
+bool OffscreenCanvas::isAccelerated() const
+{
+    return m_context && m_context->isAccelerated();

[xlai (Olivia), 2016/09/23 20:48:04]

Just want to let you know that in my previous patch I remove the
OffscreenCanvasRenderingContext2D::isAccelerated() overriding function based on
suggestion. So this function here may not return correct value
of Offscreen 2d context.

+}
+
 OffscreenCanvasFrameDispatcher* OffscreenCanvas::getOrCreateFrameDispatcher()
 {
     if (!m_frameDispatcher) {
         // The frame dispatcher connects the current thread of OffscreenCanvas
         // (either main or worker) to the browser process and remains unchanged
         // throughout the lifetime of this OffscreenCanvas.
         m_frameDispatcher = wrapUnique(new OffscreenCanvasFrameDispatcherImpl(m_clientId, m_localId, m_nonce, width(), height()));
     }
     return m_frameDispatcher.get();
 }
 
 DEFINE_TRACE(OffscreenCanvas)
 {
     visitor->trace(m_context);
 }
 
 } // namespace blink