Make GrConvolutionEffect only support Gaussian kernels and rename.

Change-Id: Ia874ad5bacc550b7ecec579719242e3354dca34b
Reviewed-on: https://skia-review.googlesource.com/7432
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
5 files changed