Change ScalarTo256 to more efficient implementation.

src/core/SkDraw.cpp

Index: src/core/SkDraw.cpp
diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index e205ee45c07dec544b10020ec41a6b80c658d7f5..d07bcb8fcf1e05364ea900a573081a32aabe1227 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -1761,14 +1761,7 @@ bool SkTriColorShader::TriColorShaderContext::setup(const SkPoint pts[], const S
 #include "SkComposeShader.h"
 
 static int ScalarTo256(SkScalar v) {
-    int scale = SkScalarToFixed(v) >> 8;
-    if (scale < 0) {
-        scale = 0;
-    }
-    if (scale > 255) {
-        scale = 255;
-    }
-    return SkAlpha255To256(scale);
+    return static_cast<int>(SkScalarPin(v, 0, 1) * 256);
 }