Merge .window.js/.worker.js/.any.js

[zcorpan]

I think it's a bit confusing how the three kinds of tests are subtly different, and I imagine that new contributors can be similarly confused.

I have two ideas for possible improvement:

• Use only .any.js and update the tests accordingly.
• Still use the 3 filename conventions, but make it more consistent how to write each kind of test (e.g. include GLOBAL in .window.js and .worker.js).

The first would simplify the implementation, the second could be slightly more convenient for test authors.

[annevk]

I kinda like window.js. It seems silly that worker.js currently requires importScripts("/resources/testharness.js"); at the top though.

[inexorabletash]

worker.js also requires a done(); at the end.

(Came here to file a bug proposing that we fix worker.js and update the tests.)