RFR (S): 8237857: LogDecorations::uptimenanos is implemented incorrectly

[Kim Barrett]

> On Jan 29, 2020, at 12:13 AM, David Holmes <david.holmes at oracle.com> wrote:
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8237857
> Webrev: http://cr.openjdk.java.net/~dholmes/8237857/webrev/

Looks good.