This provides the basic support for aggregating stats into useful metrics,
utilizing tags.
This change also adds the standard rpc metrics for the stats the jsonrpc2 system
is already filling in.
Change-Id: Ibe1b64c4c4c587dacd53112454606634e9f682ce
Reviewed-on: https://go-review.googlesource.com/c/tools/+/185342
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
