Change SkUnitScalarClampToByte to more accurate implementation.

src/effects/GrCircleBlurFragmentProcessor.cpp

Index: src/effects/GrCircleBlurFragmentProcessor.cpp
diff --git a/src/effects/GrCircleBlurFragmentProcessor.cpp b/src/effects/GrCircleBlurFragmentProcessor.cpp
index f319e3d90fc1863805b44be9d784c1b07a1b478c..f5073a520ae98ff11881b16f3ff6f6804ee34578 100644
--- a/src/effects/GrCircleBlurFragmentProcessor.cpp
+++ b/src/effects/GrCircleBlurFragmentProcessor.cpp
@@ -175,7 +175,7 @@ static uint8_t eval_at(float t, float halfWidth, float* halfKernel, int kernelWH
         }
     }
 
-    return SkUnitScalarClampToByte(acc);
+    return static_cast<uint8_t>(SkTPin(acc, 0.0f, 1.0f) * 255);
 }
 
 static inline void compute_profile_offset_and_size(float halfWH, float sigma,