Implement convertToBlob() in OffscreenCanvas

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

 // 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.
 
 #ifndef OffscreenCanvasRenderingContext2D_h
 #define OffscreenCanvasRenderingContext2D_h
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
@@ skipping 33 matching lines @@
   ContextType getContextType() const override { return Context2d; }
   bool is2d() const override { return true; }
   void setOffscreenCanvasGetContextResult(OffscreenRenderingContext&) final;
   void setIsHidden(bool) final { ASSERT_NOT_REACHED(); }
   void stop() final { ASSERT_NOT_REACHED(); }
   void setCanvasGetContextResult(RenderingContext&) final {}
   void clearRect(double x, double y, double width, double height) override {
     BaseRenderingContext2D::clearRect(x, y, width, height);
   }
   PassRefPtr<Image> getImage(AccelerationHint, SnapshotReason) const final;
+  ImageData* toImageData(SnapshotReason) const override;
 
   // BaseRenderingContext2D implementation
   bool originClean() const final;
   void setOriginTainted() final;
   bool wouldTaintOrigin(CanvasImageSource*, ExecutionContext*) final;
 
   int width() const final;
   int height() const final;
 
   bool hasImageBuffer() const final;
@@ skipping 37 matching lines @@
 
 DEFINE_TYPE_CASTS(OffscreenCanvasRenderingContext2D,
                   CanvasRenderingContext,
                   context,
                   context->is2d() && context->getOffscreenCanvas(),
                   context.is2d() && context.getOffscreenCanvas());
 
 }  // namespace blink
 
 #endif  // OffscreenCanvasRenderingContext2D_h