Make ImageBitmap Transferable

third_party/WebKit/LayoutTests/fast/canvas/resources/canvas-ImageBitmap-transferable.js

+self.onmessage = function(e) {
+  // Worker does two things:
+  // 1. call createImageBitmap() from the ImageBitmap that is transfered
+  // from the main thread

[Justin Novosad, 2015/10/23 13:30:04]

Explain why. I imagine it is to get test coverage for calling
createImageBitmap(ImageBitmap) in a worker? This aspect should be part of the
test description.

+  // 2. send the created ImageBitmap back to the main thread, the
+  // main thread exam the property of this ImageBitmap to make sure
+  // the transfer between main and worker thread didn't lose data
+  createImageBitmap(e.data.data).then(imageBitmap => {
+    postMessage({data: imageBitmap}, [imageBitmap]);
+  });
+};