Add special case circle blur for Ganesh

include/core/SkColor.h

Index: include/core/SkColor.h
diff --git a/include/core/SkColor.h b/include/core/SkColor.h
index 1ba1331c1a7261f3faaba32002dc113ac9ed0397..441f47a6e301d84ad9b1644ad5dc4cd264cb349d 100644
--- a/include/core/SkColor.h
+++ b/include/core/SkColor.h
@@ -139,6 +139,16 @@ static inline SkColor SkHSVToColor(const SkScalar hsv[3])
     return SkHSVToColor(0xFF, hsv);
 }
 
+static inline U8CPU SkUnitScalarToByte(SkScalar x) {
+    if (x < 0) {
+        return 0;
+    }
+    if (x >= SK_Scalar1) {
+        return 255;
+    }
+    return SkScalarToFixed(x) >> 8;

[bsalomon, 2015/09/11 13:05:46]

Maybe SkUnitScalarClampToByte(). Many of our SkXToY functions just assert that
the X fits in the Y.

[robertphillips, 2015/09/11 15:55:34]

Done.

[reed1, 2015/09/11 18:47:11]

Independent of the clamping question...

This is a recent hot-topic for me. What *is* the right scaling function?

1. round(x * 255)
2. floor(x * 255.9999)

The current impl is "close" to #2, but not exactly either.

[robertphillips, 2015/09/15 16:35:06]

It seems like some pinned version of #2 would be best for this use case.

+}
+
 ////////////////////////////////////////////////////////////////////////
 
 /** 32 bit ARGB color value, premultiplied. The byte order for this value is