Reland of Allow canvases to be GPU-accelerated in Workers

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp

 // Copyright 2016 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 "modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h"
 
 #include "bindings/modules/v8/OffscreenCanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContext.h"
 #include "core/frame/ImageBitmap.h"
 #include "core/frame/Settings.h"
 #include "core/workers/WorkerGlobalScope.h"
@@ skipping 65 matching lines @@
     return getOffscreenCanvas()->height();
 }
 
 bool OffscreenCanvasRenderingContext2D::hasImageBuffer() const
 {
     return !!m_imageBuffer;
 }
 
 static bool shouldAccelerate(IntSize surfaceSize)
 {
-    if (!isMainThread())
-        return false; // Add support on Workers crbug.com/
     return RuntimeEnabledFeatures::accelerated2dCanvasEnabled();
 }
 
 ImageBuffer* OffscreenCanvasRenderingContext2D::imageBuffer() const
 {
     if (!m_imageBuffer) {
         IntSize surfaceSize(width(), height());
         OpacityMode opacityMode = hasAlpha() ? NonOpaque : Opaque;
         std::unique_ptr<ImageBufferSurface> surface;
         if (shouldAccelerate(surfaceSize)) {
@@ skipping 14 matching lines @@
     }
 
     return m_imageBuffer.get();
 }
 
 ImageBitmap* OffscreenCanvasRenderingContext2D::transferToImageBitmap(ExceptionState& exceptionState)
 {
     if (!imageBuffer())
         return nullptr;
     sk_sp<SkImage> skImage = m_imageBuffer->newSkImageSnapshot(PreferAcceleration, SnapshotReasonTransferToImageBitmap);
-    DCHECK(isMainThread() || !skImage->isTextureBacked()); // Acceleration not yet supported in Workers
     RefPtr<StaticBitmapImage> image = StaticBitmapImage::create(std::move(skImage));
     image->setOriginClean(this->originClean());
     m_imageBuffer.reset(); // "Transfer" means no retained buffer
     m_needsMatrixClipRestore = true;
     return ImageBitmap::create(image.release());
 }
 
 PassRefPtr<Image> OffscreenCanvasRenderingContext2D::getImage(SnapshotReason reason) const
 {
     if (!imageBuffer())
@@ skipping 68 matching lines @@
 bool OffscreenCanvasRenderingContext2D::isContextLost() const
 {
     return false;
 }
 
 bool OffscreenCanvasRenderingContext2D::isPaintable() const
 {
     return this->imageBuffer();
 }
 }