Add unit test for clear bug

Bug: 768134
Change-Id: Ifb5a0eaeb85a8f399204467c22d0845d630d0d3d
Reviewed-on: https://skia-review.googlesource.com/60562
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed