Add GM image test for blur with clamp mode.

Adding a GM (Golden Master) image test in Skia to reproduce the bleed
black issue in Chrome. This would allow regressions to be caught in
Skia's status page before being rolled into Chrome.

Bug: 622128
Change-Id: Ifd2824fff59483c8e4be48392ba467414d41ca13
TEST=imageblurclampmode.cpp
Reviewed-on: https://skia-review.googlesource.com/20778
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
2 files changed