This adds a package for dealing with stacks in tests.
The only function at this time is NoLeak which verifies that a test
does not leak any goroutines, and prints a stack summary if it does.
Change-Id: I284b846f422334b745bef0e96d84138295120a62
Reviewed-on: https://go-review.googlesource.com/c/tools/+/232681
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
