Make OffscreenCanvas Transferable

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

Index: third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
index 0aedca56e420feed6780983a749a355e6a8f3cd2..2d2070332e5829d683c7d9bfebbb00dfd6bb023e 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
@@ -14,7 +14,8 @@
 namespace blink {
 
 OffscreenCanvas::OffscreenCanvas(const IntSize& size)
-    : m_size(size)
+    : m_canvasId(-1) // DOMNodeIds starts from 0, using -1 to indicate no associated canvas element.
+    , m_size(size)
 { }
 
 OffscreenCanvas::~OffscreenCanvas()
@@ -35,6 +36,13 @@ void OffscreenCanvas::setHeight(unsigned height)
     m_size.setHeight(clampTo<int>(height));
 }
 
+void OffscreenCanvas::setNeutered()
+{
+    m_isNeutered = true;

[Justin Novosad, 2016/04/12 18:10:23]

Add "ASSERT(!m_context);"

[xidachen, 2016/04/12 19:35:14]

Done.

+    m_size.setWidth(0);

[Justin Novosad, 2016/04/12 18:10:23]

Why do we need to reset m_size? This has observable side-effects in JS.

[xidachen, 2016/04/12 19:35:14]

When an offscreenCanvas gets transferred to worker, it is neutered, shouldn't
its size be 0?

+    m_size.setHeight(0);
+}
+
 OffscreenCanvasRenderingContext2D* OffscreenCanvas::getContext(const String& id, const CanvasContextCreationAttributes& attributes)

[Justin Novosad, 2016/04/12 18:10:23]

This method need to throw an InvalidStateError exception if the object is
neutered. And there should be a test to cover this case.

[xidachen, 2016/04/12 19:35:14]

Done.

 {
     OffscreenCanvasRenderingContext::ContextType contextType = OffscreenCanvasRenderingContext::contextTypeFromId(id);
@@ -107,7 +115,6 @@ void OffscreenCanvas::registerRenderingContextFactory(PassOwnPtr<OffscreenCanvas
 DEFINE_TRACE(OffscreenCanvas)
 {
     visitor->trace(m_context);
-    visitor->trace(m_canvas);
 }
 
 } // namespace blink