Add more layout test cases to createImageBitmap

Comparing Firefox's layout tests against Chrome's, we find that there are
two cases that is currently missing in our code base.

1). createImageBitmap from a neutered ImageBitmap.
2). createImageBitmap from a Blob object that is created by canvas.toBlob

This CL adds these two test cases.

Review URL: https://codereview.chromium.org/1589923002

Cr-Commit-Position: refs/heads/master@{#369443}
4 files changed