Improve comments for Analysis::IsSelfAssignment.

Change-Id: I34353769f4c65bdfa7205d460671a78f3463a5f2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/378317
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed