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..160307ad0acca6be77d8ae8fc19a90684652a995 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 with context");

[Justin Novosad, 2016/03/29 20:32:58]

"with context" -> "that has a rendering context."  (don't forget the period)

[xidachen, 2016/03/30 13:32:30]

Done.

+        return nullptr;
+    }
+    OffscreenCanvas* offscreenCanvas = OffscreenCanvas::create(canvas.width(), canvas.height());
+    offscreenCanvas->setOriginatedCanvas(&canvas);

[Justin Novosad, 2016/03/29 20:32:58]

Please add a unit test for this.  Test should create an HTMLCanvasElement (it's
a bit tricky see the first "paragraph" of CanvasRenderingContext2DTest::SetUp),
call this method and verify m_canvas.

[xidachen, 2016/03/30 13:32:30]

Done.

+    return offscreenCanvas;
+}
+
 }