Automatically add an environement prefix to test name

Originally posted as https://github.com/w3c/testharness.js/issues/168 by @abreton on 15 Dec 2015, 13:37 UTC:

It would be nice to run some javascript tests in different environments (windows, workers, service workers) without duplicating html files. The idea is to have a js file with all the tests written in it and then running them in different environment from the same html file.
For example if we use a test.js which has a test named test1. We could have something like this in the html file:

    <script src="test.js"></script>
    <script>
      fetch_tests_from_worker(new Worker("test.js"));
      fetch_tests_from_worker(new SharedWorker("test.js", "mySharedWorker" ));
    </script>

Then testharness could rename each test in order to have different names depending on environment, e.g.:

Result	Test Name	Message
PASS	Test1
PASS	[Worker] Test1
PASS	[SharedWorker] Test1

Start from the issue's proposed test.js usage and the fetch_tests_from_worker calls for Worker and SharedWorker environments. Trace how test names are collected and reported, then verify that each environment receives the requested prefix while the original test keeps its existing name. Done means the result table distinguishes the environments without duplicating HTML files.