internal/trace/v2: redefine NoTask and add BackgroundTask
The v2 trace parser currently handles task inheritance and region task
association incorrectly. It assumes that a TaskID of 0 means that there
is no task. However, this is only true for task events. A TaskID of 0
means that a region gets assigned to the "background task." The parser
currently has no concept of a "background task."
Fix this by defining the background task as task ID 0 and redefining
NoTask to ^uint64(0). This aligns the TaskID values more closely with
other IDs in the parser and also enables disambiguating these two cases.
For #60773.
For #63960.
Change-Id: I09c8217b33b87c8f8f8ea3b0203ed83fd3b61e11
Reviewed-on: https://go-review.googlesource.com/c/go/+/543019 Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Bypass: Michael Knyszek <mknyszek@google.com>