fix mapRect to always return the same as rectStaysRect

Bug: skia:
Change-Id: I7c19703613b3173942a12153b30e9951f35c0008
Reviewed-on: https://skia-review.googlesource.com/61820
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed