Calling `read(filename, 'binary')` should return an ArrayBuffer like
SpiderMonkey does. It is possible to call `readbuffer` instead, but that
function is not available in the SpiderMonkey JS shell.

BUG=v8:6464
R=bradnelson@chromium.org

Review-Url: https://codereview.chromium.org/2922353002
Cr-Commit-Position: refs/heads/master@{#45776}