add stages to colorfiltershader

Interestingly, this public api (makeWithColorFilter) is only used internally by
the legacy raster blitters. Perhaps we could remove/hide it?
... and that API is the only way we create one of these shaders.

Bug: skia:
Change-Id: I9bbd3786160844c963a78663e503e08122183701
Reviewed-on: https://skia-review.googlesource.com/18230
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed