Update some Sk4px APIs.

Mostly this is about ergonomics, making it easier to do good operations and hard / impossible to do bad ones.

- SkAlpha / SkPMColor constructors become static factories.
- Remove div255TruncNarrow(), rename div255RoundNarrow() to div255().  In practice we always want to round, and the narrowing to 8-bit is contextually obvious.
- Rename fastMulDiv255Round() approxMulDiv255() to stress it's approximate-ness over its speed.  Drop Round for the same reason as above... we should always round.
- Add operator overloads so we don't have to keep throwing in seemingly-random Sk4px() or Sk4px::Wide() casts.
- use operator*() for 8-bit x 8-bit -> 16-bit math.  It's always what we want, and there's generally no 8x8->8 alternative.
- MapFoo can take a const Func&.  Don't think it makes a big difference, but nice to do.

BUG=skia:

Review URL: https://codereview.chromium.org/1202013002

1 files changed, 1 insertions, 1 deletions

diff --git a/src/opts/Sk4px_SSE2.h b/src/opts/Sk4px_SSE2.h
index ee58c38ab0..74ccffc277 100644
--- a/src/opts/Sk4px_SSE2.h
+++ b/src/opts/Sk4px_SSE2.h
@@ -7,7 +7,7 @@
 
 namespace { // See Sk4px.h
 
-inline Sk4px::Sk4px(SkPMColor px) : INHERITED(_mm_set1_epi32(px)) {}
+inline Sk4px Sk4px::DupPMColor(SkPMColor px) { return Sk16b(_mm_set1_epi32(px)); }
 
 inline Sk4px Sk4px::Load4(const SkPMColor px[4]) {
     return Sk16b(_mm_loadu_si128((const __m128i*)px));