spec updates: Perf Timeline, Nav Timing, Resource Timing

Added note to clarify that perf timeline is async:
- https://w3c.github.io/performance-timeline/#sec-performance-timeline

Landed nextHopProtocol in Nav Timing and Resource Timing:
-
https://w3c.github.io/navigation-timing/#dom-performancenavigationtiming-nexthopprotocol
-
https://w3c.github.io/resource-timing/#dom-performanceresourcetiming-nexthopprotocol

While working on above, stumbled over and fixed an off-by-one error in NT
processing model:
- https://github.com/w3c/navigation-timing/issues/8

Landed {transfer, encodedBody, decodedBody}Size in Nav Timing and Resource
Timing:
-
https://w3c.github.io/navigation-timing/#dom-performancenavigationtiming-transfersize
-
https://w3c.github.io/resource-timing/#dom-performanceresourcetiming-transfersize

Please take a look at the language and associated processing model updates.
Let me know if there are any issues!

ig