See summary.
Created attachment 28140 [details] Proposed fix.
Created attachment 28141 [details] Proposed fix.
The test contained in here are a "down payment". They are just enough to verify some very basic functionality. Subsequent check-ins will contain other tests for xhr in workers.
Comment on attachment 28141 [details] Proposed fix. r=me Please add this new directory to Skipped lists for platforms that don't have workers enabled.
Committed as r41344.