github Issue #174: Tweaking the getUserMedia() algorithm

Hi

This is summary of the discussion in github issue #174.

We propose to
- move steps 3.1 and 3.2, of the getUserMedia() algorithm, to the 
synchronous section of the algorithm.
- remove the step labeled "Error Task" and inline the corresponding 
information where needed instead. This task used to contains more 
information when callbacks were used.

See [1] for more details.

/Adam

[1] https://github.com/w3c/mediacapture-main/issues/174