Fix padding bug in SkTileImageFilter.

When padding an image out to tile size, use the filter input, not the
source primitive.

NOTE: this will affect the tileimagefilter GM (new test case & size).

R=robertphillips@google.com
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1853803003

Review URL: https://codereview.chromium.org/1853803003
2 files changed