Optimisation - Only check browser compatability once
Optimisation - Only check browser compatability once

Disable use of more accurate timer temporarilly due to performance.
However, with the rearrange and introduction of the 'nowObj' it turns
out most of the delay is in resolving 'self.performance'... so keeping
this cached in nowObj actually mitigates most of the delay.

LLK/scratch-vm,LLK/scratch-vm,LLK/scratch-vm