Fix bug in raster implementation of SkRRectsGaussianEdgeMaskFilter

The bug was the raster version didn't correctly handle the CTM.

This CL also adds a way to test the behavior (by translating the
reveal GM around in SampleApp)

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3729

Change-Id: Iaacc905167d20b453203307e5ef840f552fdbb38
Reviewed-on: https://skia-review.googlesource.com/3729
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
2 files changed