Track line reachability on a step-by-step basis.

Since we know the entire flow of execution ahead of time, at any point
during trace playback, we can know if a line will be reached again or
not. We no longer highlight lines as reachable (or allow setting
breakpoints) if the line will not be reached again during trace
playback.

Change-Id: Iff563b13e2f6efb5d4f2ff37215f2ff4fb5945ed
Bug: skia:12666
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/486496
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
4 files changed