cmd/trace: include P info in goroutine slices
cmd/trace: include P info in goroutine slices

The task-oriented trace view presents the execution trace organized
based on goroutines. Often, which P a goroutine was running on is
useful, so this CL includes the P ids in the goroutine execution slices.

R=go1.11

Change-Id: I96539bf8215e5c1cd8cc997a90204f57347c48c8
Reviewed-on: https://go-review.googlesource.com/90221
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

nawawi/go,CAFxX/go,codestation/go,Cofyc/go,codestation/go,CAFxX/go,josharian/go,akutz/go,josharian/go,josharian/go,cloudflare/go,josharian/go,cloudflare/go,cloudflare/go,nawawi/go,josharian/go,nawawi/go,cloudflare/go,codestation/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,Cofyc/go,CAFxX/go,CAFxX/go,josharian/go,nawawi/go,nawawi/go,Cofyc/go,Cofyc/go,Cofyc/go,CAFxX/go,Cofyc/go,nawawi/go,josharian/go,codestation/go,akutz/go,golang/go,akutz/go,golang/go,Cofyc/go,Cofyc/go,codestation/go,golang/go,akutz/go,cloudflare/go,akutz/go,golang/go,cloudflare/go,josharian/go,akutz/go,golang/go,golang/go,golang/go,nawawi/go,codestation/go,cloudflare/go,codestation/go,akutz/go,nawawi/go,codestation/go,akutz/go,CAFxX/go