Ensure the esnext build works in therubyracer.

therubyracer, using libv8, has a more empty environment than node. The browserified esnext script expects to find some object to hook onto, but cannot since `window`, `global`, and `self` are all undefined. There is a global `this`, however, so we use that. This same problem happens in JavaScriptCore.
v0.10.1.