Fix clipped lighting image filters.

The CPU path for lighting image filters was not adjusting the filter
matrix to accommodate srcOffset, resulting in incorrectly-positioned
lights.  (The GPU path was doing this correctly.)

This change adds a new test case to the imagefiltersclipped GM,
so it will need new baselines.

BUG=skia:

Review URL: https://codereview.chromium.org/1310053004
2 files changed