Fix viewer assert in onResize

Bug: skia:
Change-Id: I99f938c76aa08a43bdc2e0fa2ad2bb04f103d2fb
Reviewed-on: https://skia-review.googlesource.com/146941
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed