Manage Mac paint events more directly.

Trying to shuttle our paint events through the Mac event system seems
to be causing a number of problems, one being that we're refreshing
too often. This works around that by tracking the invalidation flag
per window.

Bug: skia:8737
Change-Id: Ib1b8041f1d9299ff366747831a466439bfd0db29
Reviewed-on: https://skia-review.googlesource.com/c/190673
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
5 files changed