Background workers tests

Background workers with direct algoritm (one for an image) are used to accelerate the page start up. Test without workers starts much slower on Tegra 3.

It is difficult to test JS workers performance:
1. In Firefox 24 a bit heavier worker with the boundary tracing algorithm is 1.5 times slower than the same script without workers yet.
2. In Firefox 26 (Alpha) both tests have the same 1.5 times slower performance (shall I test Beta? :)
3. In Chrome 29 and 32 both tests have similar performance (a bit slower then in Firefox) and I can't test workers off-line in Chrome.

updated 26 Sep 2013