Optimize SkTileImageFilter in an offset filter when possible.

If the srcRect and dstRect have the same size, tiling will have the
same effect as an offset filter cropped to the intersection of
srcRect and dstRect. So do that instead.

BUG=569950
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1578983002

Review URL: https://codereview.chromium.org/1578983002
1 file changed