Apply additional clipping in SkGpuBlurUtils.

Clip the input src bounds to reduce the amount of rescaling work

Avoid creating redundant columns in the y-pass of two pass blur.

Change-Id: Ib1a07334dce8ca941cce0be74657eda150591b63
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290823
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
3 files changed