SkColorCubeFilter_opts: rounding is actually free here.

src/opts/SkColorCubeFilter_opts.h

Index: src/opts/SkColorCubeFilter_opts.h
diff --git a/src/opts/SkColorCubeFilter_opts.h b/src/opts/SkColorCubeFilter_opts.h
index afd6149cffaf27c003196a49d66c2dc13a684d29..3eb243de55332732345f4f1c14e2170bd7a64c7c 100644
--- a/src/opts/SkColorCubeFilter_opts.h
+++ b/src/opts/SkColorCubeFilter_opts.h
@@ -50,7 +50,7 @@ void color_cube_filter_span(const SkPMColor src[],
         const int i10 = (colorToIndex[1][g] + colorToIndex[0][b] * dim) * dim;
         const int i11 = (colorToIndex[1][g] + colorToIndex[1][b] * dim) * dim;
 
-        Sk4f color(0,0,0,0);
+        Sk4f color(0.5f);  // Starting from 0.5f gets us rounding for free.
         for (int x = 0; x < 2; ++x) {
             const int ix = colorToIndex[x][r];