Implement HTMLCanvasElement's transferControlToOffscreen

third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp

Index: third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp
diff --git a/third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp b/third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp
index 09f992f2cf01f9b7b3e18e551a876c3e9d171f26..7988132932fe846834bb47e377a9b4324e3b9a8f 100644
--- a/third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp
+++ b/third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp
@@ -17,4 +17,15 @@ void HTMLCanvasElementModule::getContext(HTMLCanvasElement& canvas, const String
     }
 }
 
+OffscreenCanvas* HTMLCanvasElementModule::transferControlToOffscreen(HTMLCanvasElement& canvas, ExceptionState& exceptionState)
+{
+    if (canvas.renderingContext()) {
+        exceptionState.throwDOMException(InvalidStateError, "Cannot transfer control from a canvas that has a rendering context.");
+        return nullptr;
+    }
+    OffscreenCanvas* offscreenCanvas = OffscreenCanvas::create(canvas.width(), canvas.height());
+    offscreenCanvas->setAssociatedCanvas(&canvas);
+    return offscreenCanvas;
+}
+
 }