Audio latency from Chrome on ChromeOS is higher than desirable. We should investigate the source of latency, and take steps to reduce it.

I've run some initial tests to compare latency on a MacBook Pro and a couple of chromebooks, results here:
https://docs.google.com/spreadsheets/d/1HDrVZUeU0fCHM2Ja0Wc5LhoUFOpfsN745cjUH6Ki44o/edit?usp=sharing

The TL;DR is:

- Web audio latency on eve is comparable to the MacBook; in both cases, Chrome itself appears to be the biggest source of latency.
- Latency on kevin is significantly higher than eve
- Safari latency is a little lower than Chrome on MacBook 

Next steps:
- figure out if ARM vs x86 is the relevant difference between kevin and eve [causing the extra latency]
- if so, figure out if increased latency is due to Chrome on ARM, or ChromeOS on ARM

Request from wuchengli: 
Set up a JavaScript loopback latency test to automatically measure web audio latency across all boards.