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/90221Reviewed-by: Heschi Kreinick <heschi@google.com>