Implement HTMLCanvasElement's transferControlToOffscreen

third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.h

 // 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.
 
 #ifndef OffscreenCanvas_h
 #define OffscreenCanvas_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/ScriptWrappable.h"
+#include "core/html/HTMLCanvasElement.h"
 #include "modules/ModulesExport.h"
 #include "platform/geometry/IntSize.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class CanvasContextCreationAttributes;
 class ImageBitmap;
 class OffscreenCanvasRenderingContext;
 class OffscreenCanvasRenderingContext2D;
@@ skipping 10 matching lines @@
     unsigned height() const { return m_size.height(); }
     void setWidth(unsigned);
     void setHeight(unsigned);
 
     // API Methods
     OffscreenCanvasRenderingContext2D* getContext(const String&, const CanvasContextCreationAttributes&);
     PassRefPtrWillBeRawPtr<ImageBitmap> transferToImageBitmap(ExceptionState&);
 
     IntSize size() const { return m_size; }
     OffscreenCanvasRenderingContext2D* renderingContext() const;
+    void setAssociatedCanvas(HTMLCanvasElement* canvas) { m_canvas = canvas; }
+    HTMLCanvasElement* getAssociatedCanvas() const { return m_canvas; }

[haraken, 2016/04/01 14:28:44]

Is this method used only by testing code? Or do you plan to use the method in
some places in a follow-up CL?

[xidachen, 2016/04/01 14:46:02]

I believe that this method will be needed in a future CL when making the
OffscreenCanvas transferable. What I have in mind is something like
HeapVector<WeakMember<HTMLCanvasElement>, 1> and this HeapVector stores pointers
to the m_canvas. Does that make sense?

[haraken, 2016/04/01 14:57:56]

You need to HeapHashMap since HeapVector cannot contain weak members though.

 
     static void registerRenderingContextFactory(PassOwnPtr<OffscreenCanvasRenderingContextFactory>);
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     OffscreenCanvas(const IntSize&);
 
     using ContextFactoryVector = Vector<OwnPtr<OffscreenCanvasRenderingContextFactory>>;
     static ContextFactoryVector& renderingContextFactories();
     static OffscreenCanvasRenderingContextFactory* getRenderingContextFactory(int);
 
     Member<OffscreenCanvasRenderingContext> m_context;
+    WeakMember<HTMLCanvasElement> m_canvas;

[haraken, 2016/03/31 23:24:24]

Would you elaborate on why this is WeakMember rather than Member?

Is it possible that OffscreenCanvas outlives HTMLCanvasElement?

     IntSize m_size;
 };
 
 } // namespace blink
 
 #endif // OffscreenCanvas_h