Add SkRRectsGaussianEdgeMaskFilter

SkRRectsGaussianEdgeShader will be removed once the usage of the
MaskFilter flavor has been propagated to Android

I will complete the raster implementation in a follow up CL.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3632

Change-Id: I42470b17308582b040a5db1a7283c3d717405345
Reviewed-on: https://skia-review.googlesource.com/3632
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
8 files changed